add prebuilt_kernel_modules module

prebuilt_kernel_modules is a build rule for processing and installing
kernel module files. The module files are processed by depmod to build
modules.{load|alias|deps|softdeps} files. Debug symbols are stripped
from the module files and then all the files are installed to
./lib/modules/<kernel_version> directory.

This is the Soong-equivalent of the 'build-image-kernel-modules-dir`
macro and is expected to replace it in the future.

Bug: 178980227
Test: m

Change-Id: I772ac816824921d275869e35b93a083d239a2450