aarch64: Add support for FEAT_SVE2p1.

Hi,

This patch add support for FEAT_SVE2p1 (SVE2.1 Extension) feature
along with +sve2p1 optional flag to enabe this feature.

Also support for following SVE2p1 instructions is added
addqv, andqv, smaxqv, sminqv, umaxqv, uminqv and uminqv.

Regression testing for aarch64-none-elf target and found no regressions.

Ok for binutils-master?

Regards,
Srinath.