Declare an inline method for the various backends to define based on
alignment requirements. That way backends that might take a performance
hit when data is not naturally aligned can specify the requirements.

With this requirement defined, we can then specify that SIMD values
require 16 bytes on the stack.

This also opens up the possibility of storing 32-bit values in 32-bits,
rather than the fixed kStackSlotSize.

Bug: v8:9909
Change-Id: I9f35c08cc91fb493a81af296d72a603dcafaf644
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1974961Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65675}