[AArch64][SVE] Asm: Support for CNT(B|H|W|D) and CNTP instructions.
This patch adds support for the following instructions:
CNTB CNTH - Determine the number of active elements implied by CNTW CNTD the named predicate constant, multiplied by an immediate, e.g. cnth x0, vl8, #16 CNTP - Count active predicate elements, e.g. cntp x0, p0, p1.b counts the number of active elements in p1, predicated by p0, and stores the result in x0.