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/fs/fat/fat.c b/fs/fat/fat.c
index 66d5473..b0fac5e 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -1260,3 +1260,20 @@
 {
 	return file_fat_read_at(filename, 0, buffer, maxsize);
 }
+
+int fat_read_file(const char *filename, void *buf, int offset, int len)
+{
+	int len_read;
+
+	len_read = file_fat_read_at(filename, offset, buf, len);
+	if (len_read == -1) {
+		printf("** Unable to read file %s **\n", filename);
+		return -1;
+	}
+
+	return len_read;
+}
+
+void fat_close(void)
+{
+}