This reverts commit 7dce6a26.

Reason for revert: Performance regressions for x64 Octane --no-opt

Original change's description:
> Fix speculation poisoning on x64
>
> Pointer cage reserved another register and inadvertently broke
> speculation poisoning by aliasing kSpeculationPoisonRegister with
> kInterpreterBytecodeArrayRegister (r12).
>
> This CL changes kInterpreterBytecodeArrayRegister to r11. Note that this
> changes it from being callee-save to caller-save, which required code
> reshuffling in a baseline builtin.
>
> Bug: v8:11726
> Change-Id: Ic2a1bd6b3a2cb4c480c84375dd3274f2efedc81f
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2869985
> Commit-Queue: Shu-yu Guo <syg@chromium.org>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Georg Neis <neis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#74364}

TBR=leszeks@chromium.org

Bug: v8:11726
Change-Id: Ic59b602e5519b05ad06890e409761f5138230b92
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2886544Reviewed-by: Shu-yu Guo <syg@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#74491}