slimbus: Add snapshot of slimbus driver

This snapshot is taken as of msm-4.19 'commit <f08e34e48e72>
(Merge "defconfig: enable dcvs configs for bengal target")'.

Change-Id: I2f187a74814b1b04fa447a5664c5b170d075ffa4
Signed-off-by: Prudhvi Yarlagadda <pyarlaga@codeaurora.org>