powerpc: Add missing CFI register information (bug #23614)

Add CFI information about the offset of registers stored in the stack
frame.

	[BZ #23614]
	* sysdeps/powerpc/powerpc64/addmul_1.S (FUNC): Add CFI offset for
	registers saved in the stack frame.
	* sysdeps/powerpc/powerpc64/lshift.S (__mpn_lshift): Likewise.
	* sysdeps/powerpc/powerpc64/mul_1.S (__mpn_mul_1): Likewise.

Signed-off-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
Reviewed-by: Gabriel F. T. Gomes <gabriel@inconstante.eti.br>