arm: Add unwind support for mixed register lists

arm: Add unwind support for mixed register lists

	* config/tc-arm.c (parse_reg_list): Add handling of mixed register
	types.
	(reg_names): Enumerate pseudoregister according to mapped physical
	register number.
	(s_arm_unwind_save_pseudo): Modify function signature.
	(s_arm_unwind_save_core): Likewise.
	(s_arm_unwind_save_mixed): New function.
	(s_arm_unwind_save): Generate register list mask to pass to nested
	functions.
	* testsuite/gas/arm/unwind-pacbti-m.s: Expand test for mixed
 	register type lists.
 	* testsuite/gas/arm/unwind-pacbti-m.d: Likewise.
	* testsuite/gas/arm/unwind-pacbti-m-readelf.d: Likewise.