[arm64] Add missing base type to enum.

This fixes a build failure for arm64 on Windows.

Bug: v8:9564
Change-Id: I845b7687379ae12c27fa2924775553c83dc5d1ec
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1724386
Commit-Queue: Richard Townsend <richard.townsend@arm.com>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62975}

src/codegen/arm64/constants-arm64.h

@@ -762,7 +762,7 @@ enum MemBarrierOp : uint32_t {
   ISB = MemBarrierFixed | 0x00000040
 };
 
-enum SystemPAuthOp {
+enum SystemPAuthOp : uint32_t {
   SystemPAuthFixed = 0xD503211F,
   SystemPAuthFMask = 0xFFFFFD1F,
   SystemPAuthMask = 0xFFFFFFFF,