arm: Add support for new frame unwinding instruction "0xb5".

This patch adds support for Arm frame unwinding instruction "0xb5" [1]. When
an exception is taken and "0xb5" instruction is encounter during runtime
stack-unwinding, we use effective vsp as modifier in pointer authentication.
On completion of stack unwinding if "0xb5" instruction is not encountered
then CFA will be used as modifier in pointer authentication.

[1] https://github.com/ARM-software/abi-aa/releases/download/2022Q3/ehabi32.pdf

libgcc/ChangeLog:

2022-11-09  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>

	* config/arm/pr-support.c (__gnu_unwind_execute): Decode opcode
	"0xb5".