STR: fix suspend abort cause system resume by powerkey event [1/1]

STR: fix suspend abort cause system resume by powerkey event [1/1]

PD#SWPL-52156

Problem:
When suspend abort happens, device driver resume call back call
get_resume_method() which always feedback the last resume method.
It cause a wrong powerkey event report by driver resume call back.

Solution:
Clr resume method in suspend prepare notify.
Provide a stationary get_resume_reason() api.

Verify:
SC2_AH212

Change-Id: I4f6577201125af6ce93dfc36b24b4c80fd812e46
Signed-off-by: Qiufang Dai <qiufang.dai@amlogic.com>