Revert "[ptr-compr] Correct size for tagged values in GetByteWidth"

This reverts commit 57bc36aa.

Reason for revert: Frame may not be allowed accesses to half size location. Reverting as a precautionary measure.

Original change's description:
> [ptr-compr] Correct size for tagged values in GetByteWidth
> 
> Bug: v8:8477
> Change-Id: Id565bb8a4d420b715e3e89325786de699e30b22c
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1517883
> Reviewed-by: Michael Stanton <mvstanton@chromium.org>
> Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#60197}

TBR=mvstanton@chromium.org,solanes@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:8477
Change-Id: Id0482074972194d8e8c531e0ea06da762e0262b7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1523347
Auto-Submit: Santiago Aboy Solanes <solanes@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60236}

src/compiler/backend/register-allocator.cc

@@ -78,7 +78,8 @@ int GetByteWidth(MachineRepresentation rep) {
     case MachineRepresentation::kCompressedSigned:
     case MachineRepresentation::kCompressedPointer:
     case MachineRepresentation::kCompressed:
-      return kTaggedSize;
+      // TODO(ishell): kTaggedSize once half size locations are supported.
+      return kSystemPointerSize;
     case MachineRepresentation::kWord64:
     case MachineRepresentation::kFloat64:
       return kDoubleSize;