CHROMIUM: timer: add debug_msleep warnings for long sleeps

CHROMIUM: timer: add debug_msleep warnings for long sleeps

I've carried a local patch to WARN_ON() long sleeps in the past, but
I think it makes sense to just check in a slightly cleaned up version
(i.e. this) that allows boot-time selection of the level to warn for.

BUG=none
TEST=edit config.txt, add timer.debug_msleep=100, boot, watch it pop a
 few times in dmesg.

Change-Id: Ibb79dfc1dd7a08b12a14af314c593a985603f5a6
Signed-off-by: Olof Johansson <olofj@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/29424
Reviewed-by: Sameer Nanda <snanda@chromium.org>