llvm_tools: move FindChromeOSRootAbove to chroot.py

This will be used more widely in later CLs.

BUG=b:333462347
TEST=unittests

Change-Id: Icbba5f343f3e92e347785686c3bb324d53ed46b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/5460283
Reviewed-by: Ryan Beltran <ryanbeltran@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
2 files changed