Add aliases for VAND imm to VBIC ~imm

On ARM NEON, VAND with immediate (16/32 bits) is an alias to VBIC ~imm with
the same type size. Adding that logic to the parser, and generating VBIC
instructions from VAND asm files.

This patch also fixes the validation routines for NEON splat immediates which
were wrong.

Fixes PR20702.

llvm-svn: 218450