drivers: base: Add generic cross-process locking API

Add a generic locking API for situations where multiple user-space
processes and/or kernel drivers need to cooordinate access to a
shared resource such as a graphics buffer.

Change-Id: Ic0dedbad74b970d7bd1a6624a845b5b1b9847443
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>

Conflicts:

	include/linux/Kbuild