mkbp: Add support for buttons and switches.

Currently, the matrix keyboard protocol does not have support for
handling non-matrixed keys.  This commit adds support for buttons which
do not appear in the keyboard matrix as well as switches.

Additionally, the keyboard FIFO is now just a general MKBP events FIFO
which MKBP events are free to use. Now, buttons and switches wil join
the key matrix event.

BUG=chrome-os-partner:54988
BUG=chrome-os-partner:54976
BUG=chromium:626863
BRANCH=None
TEST=Flash kevin, and verify that keyboard is still functional.
TEST=make -j buildall

CQ-DEPEND=CL:358926

Change-Id: If4ada904cbd5d77823a0710d4671484b198c9d91
Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Reviewed-on: https://chromium-review.googlesource.com/358633
Commit-Ready: Aseda Aboagye <aaboagye@chromium.org>
Tested-by: Aseda Aboagye <aaboagye@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
9 files changed