[arm] Fix vmov immediate for ARMv6.
[arm] Fix vmov immediate for ARMv6.

vmov immediate was always emitting movt for some immediates wether or
not the CPU supported ARMv7.

BUG=v8:4019
LOG=n

Review URL: https://codereview.chromium.org/1160093002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#28691}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh