fs: Move ls and read methods into ext4, fat

It doesn't make a lot of sense to have these methods in fs.c. They are
filesystem-specific, not generic code. Add each to the relevant
filesystem and remove the associated #ifdefs in fs.c.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@ti.com>
diff --git a/include/ext4fs.h b/include/ext4fs.h
index 3b59d15..025a2e8 100644
--- a/include/ext4fs.h
+++ b/include/ext4fs.h
@@ -138,4 +138,7 @@
 int ext4fs_devread(int sector, int byte_offset, int byte_len, char *buf);
 void ext4fs_set_blk_dev(block_dev_desc_t *rbdd, disk_partition_t *info);
 long int read_allocated_block(struct ext2_inode *inode, int fileblock);
+int ext4fs_probe(block_dev_desc_t *fs_dev_desc,
+		 disk_partition_t *fs_partition);
+int ext4_read_file(const char *filename, void *buf, int offset, int len);
 #endif