[VE] Support (m)0 and (m)1 operands

Summary:
VE has special operands to represent 0b000...000111...111 (`(m)0`) and
0b111...111000...000 (`(m)1`) bit sequences.  This patch supports those
operands not only in machine instructions but also in DAG lowering.

Reviewed By: simoll

Differential Revision: https://reviews.llvm.org/D77769