skylake: remove CBFS_SIZE option in SoC directory

CBFS_SIZE is living as a mainboard attribute. Because
of the Kconfig include ordering the SoC *cannot* set
the default. Remove from the soc Kconfig and add a
default Kconfig for SOC_INTEL_SKYLAKE.

BUG=chrome-os-partner:43419
BRANCH=None
TEST=built glados

Original-Change-Id: I8808177b573ce8e2158c9e598dbfea9ff84b97c7
Original-Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/289833
Original-Reviewed-by: Martin Roth <martinroth@google.com>

Change-Id: Icf52d7861eee016a35be899e5486deb0924a0f3c
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/11168
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/Kconfig

@@ -353,6 +353,7 @@ config CBFS_SIZE
 	  NORTHBRIDGE_INTEL_SANDYBRIDGE_NATIVE || \
 	  NORTHBRIDGE_INTEL_NEHALEM || SOC_INTEL_BRASWELL || \
 	  SOC_INTEL_BROADWELL
+	default 0x200000 if SOC_INTEL_SKYLAKE
 	default ROM_SIZE
 	help
 	  This is the part of the ROM actually managed by CBFS, located at the