doc: cleanup after NFFS removal

Patch introduce references to LittleFS instead of NFFS where it
was suitable. In other places NFFS mentions were removed

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>

doc/guides/dts/flash_partitions.inc

@@ -228,4 +228,4 @@ File System Partitions
 ======================
 
 **storage_partition**
-  This is the area where e.g. NFFS expects its partition.
+  This is the area where e.g. LittleFS or NVS or FCB expects its partition.

doc/introduction/index.rst

@@ -135,8 +135,8 @@ Zephyr offers a large and ever growing number of features including:
    systems. A native POSIX port, lets you build and run Zephyr as a native
    application on Linux and other OSes, aiding development and testing.
 
-**Virtual File System Interface with NFFS and FATFS Support**
+**Virtual File System Interface with LittleFS and FATFS Support**
-   Newtron Flash Filesystem (NFFS) and FATFS Support,
+   LittleFS and FATFS Support,
    FCB (Flash Circular Buffer) for memory constrained applications, and
    file system enhancements for logging and configuration.
 

doc/reference/file_system/index.rst

@@ -4,7 +4,7 @@ File Systems
 ############
 
 Zephyr RTOS Virtual Filesystem Switch (VFS) allows applications to mount multiple
-file systems at different mount points (e.g., ``/fatfs`` and ``/nffs``). The
+file systems at different mount points (e.g., ``/fatfs`` and ``/lfs``). The
 mount point data structure contains all the necessary information required
 to instantiate, mount, and operate on a file system. The File system Switch
 decouples the applications from directly accessing an individual file system's
@@ -36,15 +36,10 @@ A file system is declared as:
 
 where
 
-- ``FS_FATFS`` is the file system type like FATFS or NFFS.
+- ``FS_FATFS`` is the file system type like FATFS or LittleFS.
 - ``FATFS_MNTP`` is the mount point where the file system will be mounted.
 - ``fat_fs`` is the file system data which will be used by fs_mount() API.
 
-Known Limitations
-*****************
-
-NFFS supports only one instance of file system due to the library's internal
-implementation limitation.
 
 
 Sample

drivers/flash/Kconfig.sam0

@@ -18,6 +18,6 @@ config SOC_FLASH_SAM0_EMULATE_BYTE_PAGES
 	depends on SOC_FLASH_SAM0
 	help
 	  Emulate a device with byte-sized pages by doing a
-	  read/modify/erase/write.  Needed for NFFS.
+	  read/modify/erase/write.
 
 endif

include/settings/settings.h

@@ -191,7 +191,7 @@ struct settings_handler_static {
  * Initialization of settings and backend
  *
  * Can be called at application startup.
- * In case the backend is NFFS Remember to call it after FS was mounted.
+ * In case the backend is a FS Remember to call it after the FS was mounted.
  * For FCB backend it can be called without such a restriction.
  *
  * @return 0 on success, non-zero on failure.