Same operations are done in ish_hw_start() and _ish_hw_reset() to
wakeup ISH device. Consolidate them by introducing a new function
ish_wakeup() and move the code there.

Signed-off-by: Even Xu <even.xu@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>