log: symbolic levels, H2K_LOG_NO_SPAM mode, and bitmask once_ht

Three improvements to the logging system:

1. Accept symbolic level names in LOGBUF syntax (err, warn, info, dbg) in
   addition to numeric values (0, 1, 2, 3):
     make LOGBUF=1[warn]           whole kernel, WARN and above
     make LOGBUF=sched[info]       sched directory, INFO and above
     make LOGBUF=futex[err],sched[dbg]  mixed symbolic and numeric

2. Add H2K_LOG_NO_SPAM mode to strip spam-control macros (once/throttle) and
   make them no-ops. Eliminates static state bloat:
     make LOGBUF=1[warn] H2K_LOG_NO_SPAM=1

   In this mode, H2K_log_once/throttle macros become empty (no-op), while
   base H2K_log/err/warn/info/dbg macros still emit normally.

3. Optimize H2K_log_once_ht to use a single u32 bitmask instead of an array.
   Each hardware thread's once-flag is now a single bit in a shared u32,
   reducing per-callsite memory from MAX_HTHREADS*4 bytes to 4 bytes.
   Uses H2K_atomic_setbit for race-free per-bit access. Works in both
   H2K_LOGBUF and H2K_LOG_PRINTF modes.

Implemented via Makefile function for level mapping, conditional macro
redefinition in log.h, and bitmask logic in log.ref.c. Works in both kernel
(LOGBUF) and standalone test (LOG_PRINTF) builds.

Signed-off-by: Zeev Belinsky <zbelinsk@qti.qualcomm.com>

Author: zbelinsk

kernel/util/log/log.spec

@@ -0,0 +1,86 @@
+<!--
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ * SPDX-License-Identifier: BSD-3-Clause-Clear
+ -->
+
+# H2K Logging Specification
+
+## Build Configuration
+
+### LOGBUF Syntax
+
+```
+make LOGBUF=<target>[<level>]
+```
+
+- `<target>`: `1` (all), `<module>` (dir), `<file>` (filename), or comma-separated list
+- `<level>`: `0`/`err`, `1`/`warn`, `2`/`info`, `3`/`dbg` (default: `3`)
+
+Examples:
+```
+make LOGBUF=1[warn]              # whole kernel, WARN+
+make LOGBUF=sched[info]          # sched module, INFO+
+make LOGBUF=sched[warn],futex[err]  # mixed levels
+```
+
+### H2K_LOG_NO_SPAM
+
+Disables spam-control macros (once/throttle) to eliminate static state:
+```
+make LOGBUF=1[warn] H2K_LOG_NO_SPAM=1
+```
+
+When enabled, `H2K_log_once*()` and `H2K_log_throttle*()` become no-ops.
+
+## API
+
+### Base Logging
+```c
+H2K_log(fmt, ...)        // DEBUG
+H2K_log_err(fmt, ...)    // ERROR
+H2K_log_warn(fmt, ...)   // WARN
+H2K_log_info(fmt, ...)   // INFO
+H2K_log_dbg(fmt, ...)    // DEBUG
+```
+
+### Spam Control
+```c
+H2K_log_once*(fmt, ...)           // emit once per callsite (4 bytes)
+H2K_log_once_ht*(fmt, ...)        // emit once per HT (4 bytes, bitmask)
+H2K_log_throttle*(interval, ...)  // rate-limited (8 bytes)
+H2K_log_throttle_ht*(interval, ...)  // per-HT rate-limited (8×MAX_HTHREADS bytes)
+```
+
+All combinations of severity (`_err`, `_warn`, `_info`, `_dbg`) available.
+
+### String Variants
+```c
+H2K_log_string*(S)              // pre-formatted string
+H2K_log_string_once*(S)         // with spam control
+H2K_log_string_throttle*(interval, S)
+```
+
+## Output Format
+
+```
+[ht<id>][<LEVEL>][<pcycles>][<file>:<line>] message
+```
+
+Example: `[ht0][WARN][12345678][sched.c:42] reschedule timeout`
+
+## Memory
+
+| Macro | Storage |
+|-------|---------|
+| `H2K_log_once()` | 4 bytes (u32 flag) |
+| `H2K_log_once_ht()` | 4 bytes (u32 bitmask, 1 bit per HT) |
+| `H2K_log_throttle()` | 8 bytes (u64 timestamp) |
+| `H2K_log_throttle_ht()` | 8 × MAX_HTHREADS bytes |
+
+With `H2K_LOG_NO_SPAM=1`: no static state for spam-control macros.
+
+## Implementation
+
+- **H2K_LOGBUF**: lockless per-HT ring buffers, atomic setbit for once, spinlock for throttle
+- **H2K_LOG_PRINTF**: printf-based, static inline prefix helpers, same spam-control logic
+- **Silent**: all macros are no-ops (default when neither flag set)