The split of intermediate + base pointer in two maps was ugly.
This is also required for tracking bounds on pointers, required for robustness tests.

Change-Id: I782aeee8caab43ce58ba948dcca97afa2e07482c
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/29273
Presubmit-Ready: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>