CHROMIUM: mailbox: add tinysys mailbox

1. add common mailbox driver
2. add tinysys mailbox driver

BUG=None
TEST=build pass & bootup to shell.
UPSTREAM-TASK=b:379034573

Signed-off-by: Jjian Zhou <jjian.zhou@mediatek.corp-partner.google.com>
Change-Id: If57cb6e3aa9dc627dadf080132b3828ae98027c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/6073689


Commit-Queue: Fei Shao <fshao@chromium.org>
Reviewed-by: Pin-yen Lin <treapking@chromium.org>
Reviewed-by: Fei Shao <fshao@chromium.org>
Tested-by: Fei Shao <fshao@chromium.org>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Hubert Mazur <hmazur@google.com>