[AArch64] Avoid emitting MOVID when NEON is disabled

Previously, creating a zero floating-point constant used MOVID even when
NEON was disabled which resulted in the following fatal error:
`Attempting to emit MOVID instruction but the Feature_HasNEON predicate(s) are not met`

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D125237