intel_mid_powerbtn: use shared SRAM to read Powerbutton state

intel_mid_powerbtn: use shared SRAM to read Powerbutton state

BZ: 8874

switch power button read access from IPC to shared SRAM to help
reduce latency introduced by IPC call.

Change-Id: I158b6ffa5cc28f7db527e0740fb1b54d40082cf0
Signed-off-by: Zhifeng Wang <zhifeng.wang@intel.com>
Reviewed-on: http://android.intel.com:8080/24607
Reviewed-by: Gross, Mark <mark.gross@intel.com>
Tested-by: Gross, Mark <mark.gross@intel.com>