Add validateBufferSize and getTransportSize

Bug: b/131089111
Test: build, boot
Change-Id: Ie5ce20010c8a00eebde239d149faa1fb0fc07195
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/50074Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Macnak <natsu@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>