Adds basic framework to pipeline.cc to enable a seperate fast register
allocator for the TurboProp mid-tier. As part of this, common logic as
well as a base class for RegisterAllocationData is moved to a seperate
register-allocation.h header file. The current register allocator's
RegisterAllocationData is renamed to TopTierRegisterAllocationData, and
the former name is the new base class held in PipelineData.

BUG=v8:9684

Change-Id: I28285b7d6112505bf90e88ea3cda66d03dfabc74
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2295359
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68852}