soc/intel: indicate to build system that XIP_ROM_SIZE isn't used

The XIP_ROM_SIZE Kconfig variable isn't used for these chipsets.
Therefore, indicate as such so that romstage can be placed in
cbfs less rigidly.

Change-Id: If5cae10b90e05029df56c282e8adf37fa0102955
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/14626
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
diff --git a/src/soc/intel/skylake/Kconfig b/src/soc/intel/skylake/Kconfig
index 0b7dc8c..1ac0647 100644
--- a/src/soc/intel/skylake/Kconfig
+++ b/src/soc/intel/skylake/Kconfig
@@ -24,6 +24,7 @@
 	select IOAPIC
 	select MMCONF_SUPPORT
 	select MMCONF_SUPPORT_DEFAULT
+	select NO_FIXED_XIP_ROM_SIZE
 	select PARALLEL_MP
 	select PCIEXP_ASPM
 	select PCIEXP_COMMON_CLOCK