Example kernel headers header_lib package

This change is foundational for converting many modules that depend on kernel
headers built via the platform build system.

Bug: 143567008
Change-Id: I998890ed427104ed835000e421756981e0f24ab5
[rishabhb@codeaurora.org: add logic to iterate over mandatory headers
 and only generate these headers if not already present in
 usr/include/asm.]
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>