xip: Do not pass --xip for early stages if CAR supports code execution

On modern x86 platforms like apollolake, pre-RAM stages verstage and
romstage run within the cache-as-ram region. Thus, we do not need to
pass in the --xip parameter to cbfstool while adding these
stages. Introduce a new Kconfig variable NO_XIP_EARLY_STAGES which is
default false for all x86 platforms. Apollolake selects this option
since it supports code execution with CAR.

Change-Id: I2848046472f40f09ce7fc230c258b0389851b2ea
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/14623
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

Makefile.inc

@@ -798,13 +798,21 @@ ifeq ($(CONFIG_ARCH_ROMSTAGE_X86_32)$(CONFIG_ARCH_ROMSTAGE_X86_64),y)
 #
 # Make sure that segment for .car.data is ignored while adding romstage.
 $(CONFIG_CBFS_PREFIX)/romstage-align := 64
-$(CONFIG_CBFS_PREFIX)/romstage-options := --xip -S .car.data
+$(CONFIG_CBFS_PREFIX)/romstage-options := -S ".car.data"
+
+# If CAR does not support execution of code, romstage on x86 is expected to be
+# xip.
+ifneq ($(CONFIG_NO_XIP_EARLY_STAGES),y)
+$(CONFIG_CBFS_PREFIX)/romstage-options += --xip
+
 # If XIP_ROM_SIZE isn't being used don't overly constrain romstage by passing
 # -P with a default value.
 ifneq ($(CONFIG_NO_FIXED_XIP_ROM_SIZE),y)
 $(CONFIG_CBFS_PREFIX)/romstage-options += -P $(CONFIG_XIP_ROM_SIZE)
-endif
-endif
+endif    # CONFIG_NO_FIXED_XIP_ROM_SIZE
+
+endif   # CONFIG_NO_XIP_EARLY_STAGES
+endif   # CONFIG_ARCH_ROMSTAGE_X86_32 / CONFIG_ARCH_ROMSTAGE_X86_64
 
 cbfs-files-y += $(CONFIG_CBFS_PREFIX)/ramstage
 $(CONFIG_CBFS_PREFIX)/ramstage-file := $(objcbfs)/ramstage.elf