s390/fpu: let fpu_vlm() and fpu_vstm() return number of registers

s390/fpu: let fpu_vlm() and fpu_vstm() return number of registers

Let fpu_vlm() and fpu_vstm() macros return the number of registers saved /
loaded. This is helpful to read easy to read code in case there are several
subsequent fpu_vlm() or fpu_vstm() calls:

	__vector128 *vxrs = ....

	vxrs += fpu_vstm(0, 15, vxrs);
	vxrs += fpu_vstm(16, 31, vxrs);

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>