cbfstool: move iself() to eflheaders.c

The only user of iself() was in elfheaders.c. Move it there,
and make it local to the compilation unit.

Change-Id: I0d919ce372f6e2fce75885fb4fcba20d985979b3
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/5369
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Marc Jones <marc.jones@se-eng.com>

util/cbfstool/common.h

@@ -109,8 +109,6 @@ uint32_t string_to_arch(const char *arch_string);
 
 #define ALIGN(val, by) (((val) + (by)-1)&~((by)-1))
 
-int iself(unsigned char *input);
-
 typedef void (*comp_func_ptr) (char *, int, char *, int *);
 typedef enum { CBFS_COMPRESS_NONE = 0, CBFS_COMPRESS_LZMA = 1 } comp_algo;