kleaf: Move kernel_build_config to its own module.

This makes kernel.bzl smaller.

Clients are still expected to load kernel_build_config
from kernel.bzl. kernel_build_config.bzl is an implementation
detail.

Test: TH
Test: bazel build //common/... //common-modules/... --nobuild
Bug: 233156052
Change-Id: I9322a3286dc98e4313330d165ba37502d0a37eb3
1 file changed