libbinder: Add support for Trusty kernel

This adds build system support for libbinder in the trusty
kernel. The kernel needs a separate rules.mk because
trusty's userspace build system does not support all the
flags used in the existing rules.mk when building kernel
modules. When trusty fully switches to bazel these two
makefiles should get combined into one.

Bug: 230134581
Test: build Trusty
Change-Id: I1a1d2c84ab011d3f36a1c69a4acd4780ca01f75e