mhi: core: remove M1->M2 debounce timer

Older targets required a debounce delay for device to transition
into M2 before waking the device back up. We no longer need that
delay, so removing debounce logic.

CRs-Fixed: 2279751
Change-Id: Id594af9efada14bbc1c1241cf0d0b6f15896cfee
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>