PPC: only clear cr field 6 under simd AnyTrue and AllTrue

From PPC ABI:

>The condition code register fields CR0, CR1, CR5, CR6,
 and CR7 are volatile. The condition code register fields
 CR2, CR3, and CR4 are nonvolatile.

We can safely clear Cr field 6 without the need to save its
content first. Clearing the entire CR register will cause
crashes if it's not restored properly.

Change-Id: I854f5631294f56f542b1a6f4e23dd7dbcf000d7d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2810802


Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#73837}