[AArch64][SVE] Asm: Support for signed/unsigned MIN/MAX/ABD

This patch implements the following varieties:

- Unpredicated signed max,   e.g. smax z0.h, z1.h, #-128
- Unpredicated signed min,   e.g. smin z0.h, z1.h, #-128

- Unpredicated unsigned max, e.g. umax z0.h, z1.h, #255
- Unpredicated unsigned min, e.g. umin z0.h, z1.h, #255

- Predicated signed max,     e.g. smax z0.h, p0/m, z0.h, z1.h
- Predicated signed min,     e.g. smin z0.h, p0/m, z0.h, z1.h
- Predicated signed abd,     e.g. sabd z0.h, p0/m, z0.h, z1.h

- Predicated unsigned max,   e.g. umax z0.h, p0/m, z0.h, z1.h
- Predicated unsigned min,   e.g. umin z0.h, p0/m, z0.h, z1.h
- Predicated unsigned abd,   e.g. uabd z0.h, p0/m, z0.h, z1.h

llvm-svn: 336317