improve PBL->SBL EE transition handling in preparation for qwx_init_task()

improve PBL->SBL EE transition handling in preparation for qwx_init_task()

Use a custom work queue for all EE/MHI state transitions.
Running MHI state changes in the systq won't work while running the
qwx init recovery task from the same systq. The init task would wait
for a state change and time out (assuming the device had failed to load
firmware when all was well), then the MHI state change task would run.

For consistency, send wakeups for the initial PBL->SBL EE transition
from the MHI state change task rather than the interrupt handler.
This in-place wakeup was an early hack from before when state
transitions were handled properly.