st-hal: reset backend when there could be lpi mode switch

When session is in buffering and a lpi mode switch
event is triggered, session switch can be postponed
and also the backend reset is skipped.
Move the backend reset to session start whenever
lpi mode switch can happen.

Change-Id: I3ea1ef630cfac5297cb83b48d3ab29bbaaa2dd87
2 files changed