docs: mark uses_fp as deprecated in man pages

Minimal doc update for 2.9. Full refactor of component docs,
halcompile, and API removal planned for 2.10.

Ref: #3895

Author: Luca Toniolo

docs/man/man3/hal_create_thread.3hal

@@ -18,7 +18,8 @@ The name of the thread
 The interval, in nanoseconds, between iterations of the thread
 
 .IP \fIuses_fp\fR
-Must be nonzero if a function which uses floating-point will be attached to this thread.
+\fBDeprecated.\fR All threads now unconditionally save and restore
+floating-point state.  This parameter is accepted but ignored.
 
 .SH DESCRIPTION
 \fBhal_create_thread\fR establishes a realtime thread that will execute one or more HAL functions periodically.

docs/man/man3/hal_export_funct.3hal

@@ -20,8 +20,8 @@ The pointer to the function
 The argument to be passed as the first parameter of \fIfunct\fR
 
 .IP \fIuses_fp\fR
-Nonzero if the function uses floating-point operations, including assignment
-of floating point values with "=".
+\fBDeprecated.\fR All threads now unconditionally save and restore
+floating-point state, so this flag has no effect.
 
 .IP \fIreentrant\fR
 If reentrant is non-zero, the function may be preempted and called again

docs/man/man3/rtapi_task_new.3rtapi

@@ -19,7 +19,8 @@ started
 .IP \fIprio\fR
 A task priority value returned by \fBrtapi_prio_xxxx\fR
 .IP \fIuses_fp\fR
-A flag that tells the OS whether the task uses floating point or not.
+\fBDeprecated.\fR All tasks now unconditionally save and restore
+floating-point state.  This parameter is accepted but ignored.
 .IP \fItask_id\fR
 A task ID returned by a previous call to \fBrtapi_task_new\fR
 .SH DESCRIPTION

docs/man/man9/motion.9

@@ -42,7 +42,8 @@ Optionally the number of Digital I/O is set with num_dio. The number of Analog I
 Pin names starting with "\fBjoint\fR"  or "\fBaxis\fR" are are read and updated by the motion-controller function.
 
 .SH DESCRIPTION
-By default, the base thread does not support floating point.  Software stepping, software encoder counting, and software pwm do not use floating point.  \fBbase_thread_fp\fR can be used to enable floating point in the base thread (for example for brushless DC motor control).
+\fBbase_thread_fp\fR is \fBdeprecated\fR and has no effect.  All threads now
+unconditionally save and restore floating-point state.
 
 .P
 These pins and parameters are created by the realtime \fBmotmod\fR module. This module provides a HAL interface for LinuxCNC's motion planner. Basically \fBmotmod\fR takes in a list of waypoints and generates a nice blended and constraint-limited stream of joint positions to be fed to the motor drives.