log: Add a category for filesystems

Sometimes it is useful to log things related to filesystems. Add a new
category and place it at the top of one of the FAT files.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/log.h

@@ -100,6 +100,8 @@ enum log_category_t {
 	LOGC_BOOT,
 	/** @LOGC_EVENT: Related to event and event handling */
 	LOGC_EVENT,
+	/** @LOGC_FS: Related to filesystems */
+	LOGC_FS,
 	/** @LOGC_COUNT: Number of log categories */
 	LOGC_COUNT,
 	/** @LOGC_END: Sentinel value for lists of log categories */