cbfstool: Move cbfs_file_get_header to fit.c

Since fit.c is the only caller of this function move it out of common.c
and into fit.c.

Change-Id: I64cc31a6d89ee425c5b07745ea5ca9437e2f3fcf
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/14949
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

util/cbfstool/cbfs.h

@@ -254,9 +254,6 @@ static size_t widths_cbfs_hash[] unused = {
 uint32_t get_cbfs_entry_type(const char *name, uint32_t default_value);
 uint32_t get_cbfs_compression(const char *name, uint32_t unknown);
 
-/* common.c */
-void cbfs_file_get_header(struct buffer *buf, struct cbfs_file *file);
-
 /* cbfs-mkpayload.c */
 void xdr_segs(struct buffer *output,
 	      struct cbfs_payload_segment *segs, int nseg);