gas: Validate SFrame RA tracking and fixed RA offset

gas: Validate SFrame RA tracking and fixed RA offset

Verify all architectures participating in SFrame generation do define
the mandatory SFrame return address (RA) tracking predicate function
sframe_ra_tracking_p. Do so by explicitly not testing for the macro
SFRAME_FRE_RA_TRACKING as otherwise required.

Verify that architectures not using SFrame RA tracking specify a valid
fixed RA offset.

gas/
	* gen-sframe.c (output_sframe_internal): Validate SFrame
	RA tracking and fixed RA offset.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>