mhi: core: Force PM state to M0 while processing BW scaling event

Driver defers processing of BW scaling event if PM state is not in
M0. This delays the BW scaling to take effect. Fix this issue by
resuming the device if it was suspended state and assert wake DB.
After changing the BW of the link de-assert the wake DB.

Change-Id: Ibf827912a4de71d14f461382c28080157c65d6e0
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>