[ARM][gas] Fix warnings about uninitialised uses and unused const variables

	* config/tc-arm.c (fpu_arch_vfp_v1): Mark with ATTRIBUTE_UNUSED.
	(fpu_arch_vfp_v3): Likewise.
	(fpu_arch_neon_v1): Likewise.
	(arm_arch_full): Likewise.
	(parse_neon_el_struct_list): Initialize fields of firsttype.