include: gas: bfd: sframe: clean the abstraction

include: gas: bfd: sframe: clean the abstraction

... between specification and implmentation.

Move to definition in the implementation (gas/ld/libsframe) and not the
specification (include/sframe.h).  At this time the implementation in
gas and ld generate the sections in the latest SFrame version only.

Reviewed-by: Jens Remus <jremus@linux.ibm.com>
bfd/
	* elf-sframe.c: Add definition here.
gas/
	* gen-sframe.c: Likewise.
libsframe/
	* sframe.c: Likewise.
include/
	* sframe.h: Remove the definition.