Move platform abstraction to base library

Also split v8-core independent methods from checks.h to base/logging.h and
merge v8checks with the rest of checks.

The CPU::FlushICache method is moved to CpuFeatures::FlushICache

RoundUp and related methods are moved to base/macros.h

Remove all layering violations from src/libplatform

BUG=none
R=jkummerow@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/358363002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22092 ce2b1a6d-e550-0410-aec6-3dcde31c8c00