kevin: Remove KBLIGHT module

Rename KBLIGHT to BKLIGHT (and remove the unneeded CONFIG) to reflect
the actual PWM function.

BUG=None
BRANCH=None
TEST=`make buildall -j` and verify kevin boots to kernel

Change-Id: Idf6d21f096e491a62862362862e1e8a481db8987
Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/338512
Commit-Ready: Shawn N <shawnn@chromium.org>
Tested-by: Shawn N <shawnn@chromium.org>
Reviewed-by: Mary Ruthven <mruthven@chromium.org>