soc/intel/apollolake: Add function to read and clear GPE status

Implement the generic acpi_get_gpe() function to read and clear
the GPE status for a specific GPE.

Tested by watching GPE status in a loop while generating interrupts
manually from the EC console.

BUG=chrome-os-partner:53336

Change-Id: Id885e98d48c2133a868da19eca3360e2dfb82e84
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
1 file changed