soc/intel/skylake: Enable PARALLEL_MP_AP_WORK

With change a4b11e5c90 (soc/intel/skylake: Perform CPU MP Init
before FSP-S Init) to perform CPU MP init before FSP-S init, MTRR
programming was moved to be performed after CPU init is done. However,
in order to allow callbacks after MP init, PARALLEL_MP_AP_WORK needs
to be enabled. Since this option was not selected, MTRR programming
always failed in ramstage for Skylake / Kaby Lake mainboards.

BUG=b:36656098
TEST=Verified 2500+ cycles of suspend resume on poppy.

Change-Id: I22a8f6ac90ba35075ff97dd57bab66c129f3e771
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/19608
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/skylake/Kconfig

@@ -38,6 +38,7 @@ config CPU_SPECIFIC_OPTIONS
 	select NO_FIXED_XIP_ROM_SIZE
 	select MRC_SETTINGS_PROTECT
 	select PARALLEL_MP
+	select PARALLEL_MP_AP_WORK
 	select PCIEXP_ASPM
 	select PCIEXP_COMMON_CLOCK
 	select PCIEXP_CLK_PM