zephyr: Introduce Zephyr native filesystem VFS interface.

This allows using Zephyr's supported VFS and interface it to MicroPython's
VFS.  That makes the MicroPython-side filesystem drivers unecessary, eg you
can disable LFS2 in MicroPython but still do LFS2 because it's using
Zephyr's.

An advantage of this is that the filesystem can be shared between Zephyr C
code and MicroPython.

Signed-off-by: Vdragon <mail@massdriver.space>

Author: VynDragon

ports/zephyr/CMakeLists.txt

@@ -55,6 +55,7 @@ set(MICROPY_SOURCE_PORT
     uart_core.c
     zephyr_device.c
     zephyr_storage.c
+    zephyr_filesystem.c
     mpthreadport.c
 )
 list(TRANSFORM MICROPY_SOURCE_PORT PREPEND ${MICROPY_PORT_DIR}/)

ports/zephyr/README.md

@@ -208,3 +208,47 @@ run the following after you built an image with the previous command:
 
     $ west build -t run
 
+File Systems
+------------
+
+The Zephyr Micropython port provides 2 options for handling filesystems on the device:
+The first is the Micropython filesystem management, which uses Micropython's filesystem code and
+relies on zephyr's FlashArea API, this is enabled by default when 
+`CONFIG_FLASH` and `CONFIG_FLASH_MAP` are turned on.
+The second option is using Zephyr's Filesystem management:
+This relies on Zephyr's File System features and enables sharing access between zephyr and
+micropython code. Several configuration options must be enabled:
+
+    CONFIG_FLASH_MAP=y # Requirement for the file system subsystem
+    CONFIG_FILE_SYSTEM=y # Enables the file system subsystem
+    CONFIG_FILE_SYSTEM_LITTLEFS=y # Enables the littlefs support in zephyr
+    CONFIG_FILE_SYSTEM_MKFS=y # Enables the ability to create new file systems
+
+Then, a fstab must be added to the dts overlay, for example:
+
+    
+	fstab {
+		compatible = "zephyr,fstab";
+		lfs2: lfs2 {
+			compatible = "zephyr,fstab,littlefs";
+			mount-point = "/flash";
+			partition = <&storage_partition>;
+			read-size=<16>;
+			prog-size=<4096>;
+			cache-size=<4096>;
+			lookahead-size=<32>;
+			block-cycles=<4>;
+		};
+	};
+	
+It is then possible to use the FS like a normal Micropython filesystem:
+
+    import vfs, zephyr
+    zfs = zephyr.FileSystem(zephyr.FileSystem.fstab()[0])
+    vfs.mount(zfs, "/zephyr")
+
+You may disable Micropython's File system code to save space:
+    
+    CONFIG_MICROPY_VFS_FAT=n
+    CONFIG_MICROPY_VFS_LFS1=n
+    CONFIG_MICROPY_VFS_LFS2=n

ports/zephyr/modzephyr.c

@@ -86,6 +86,9 @@ static const mp_rom_map_elem_t mp_module_time_globals_table[] = {
     #ifdef CONFIG_FLASH_MAP
     { MP_ROM_QSTR(MP_QSTR_FlashArea), MP_ROM_PTR(&zephyr_flash_area_type) },
     #endif
+    #ifdef CONFIG_FILE_SYSTEM
+    { MP_ROM_QSTR(MP_QSTR_FileSystem), MP_ROM_PTR(&zephyr_filesystem_type) },
+    #endif
 };
 
 static MP_DEFINE_CONST_DICT(mp_module_time_globals, mp_module_time_globals_table);

ports/zephyr/modzephyr.h

@@ -37,4 +37,8 @@ extern const mp_obj_type_t zephyr_disk_access_type;
 extern const mp_obj_type_t zephyr_flash_area_type;
 #endif
 
+#ifdef CONFIG_FILE_SYSTEM
+extern const mp_obj_type_t zephyr_filesystem_type;
+#endif
+
 #endif // MICROPY_INCLUDED_ZEPHYR_MODZEPHYR_H

ports/zephyr/mpconfigport.h

@@ -84,9 +84,10 @@
 #endif
 #define MICROPY_PY_MACHINE_PWM      (1)
 #define MICROPY_PY_MACHINE_PWM_INCLUDEFILE "ports/zephyr/machine_pwm.c"
-#ifdef CONFIG_NETWORKING
-// If we have networking, we likely want errno comfort
+#if defined(CONFIG_NETWORKING) || defined(CONFIG_FILE_SYSTEM)
 #define MICROPY_PY_ERRNO            (1)
+#endif
+#ifdef CONFIG_NETWORKING
 #define MICROPY_PY_SOCKET           (1)
 #endif
 #ifdef CONFIG_BT