The same bit field (MiscField) is currently used to encode either a SIMD
lane size or a memory access mode depending on the instruction.

For now this does not conflict, but in order to support protected loads
and stores on arm64, we will need to add a protected access mode to some
SIMD instructions that already encode a lane size (kArm64LoadSplat,
kArm64LoadLane, kArm64StoreLane).

To prepare for this, use non-overlapping bits of the Misc field to
encode the two properties.

R=zhin@chromium.org
CC=ahaas@chromium.org

Bug: v8:11098
Change-Id: I2320b2be74d023429f8b8c78a5736b13f53c0399
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2643390
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72312}