soc/intel/apollolake: Initialize GPEs in bootblock

Initialize the GPEs from mainboard config in bootblock, so they
can be used in verstage to query latched interrupt status.

I still left it called in ramstage just to be sure that the
configuration was not overwritten in FSP stages.

Tested by reading and reporting GPE status in a loop in verstage
and manually triggering an interrupt on EC console.

BUG=chrome-os-partner:53336

Change-Id: Iacd0483e4b3229aca602bb5bb40586eedf35a6ea
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/16670
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/apollolake/bootblock/bootblock.c

@@ -182,4 +182,7 @@ void bootblock_soc_early_init(void)
 	enable_spibar();
 
 	cache_bios_region();
+
+	/* Initialize GPE for use as interrupt status */
+	pmc_gpe_init();
 }