mb/google/myst: Build for chromeOS

Adjust build configs to build Myst for chromeOS.

BUG=b:270618097
TEST=builds

Signed-off-by: Jon Murphy <jpmurphy@google.com>
Change-Id: If4b6917fe024067409bfbb3d2691c37759b5cace
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74097
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

src/mainboard/google/myst/Kconfig

@@ -8,6 +8,7 @@ if BOARD_GOOGLE_BASEBOARD_MYST
 config BOARD_SPECIFIC_OPTIONS
 	def_bool y
 	select BOARD_ROMSIZE_KB_16384
+	select MAINBOARD_HAS_CHROMEOS
 	select SOC_AMD_PHOENIX
 
 config DEVICETREE
@@ -26,4 +27,9 @@ config MAINBOARD_FAMILY
 config MAINBOARD_PART_NUMBER
 	default "Myst" if BOARD_GOOGLE_MYST
 
+config VBOOT
+	select VBOOT_NO_BOARD_SUPPORT
+	select VBOOT_SEPARATE_VERSTAGE
+	select VBOOT_STARTS_IN_BOOTBLOCK
+
 endif # BOARD_GOOGLE_BASEBOARD_MYST

src/mainboard/google/myst/Makefile.inc

@@ -6,6 +6,7 @@ romstage-y += port_descriptors.c
 
 ramstage-y += mainboard.c
 ramstage-y += port_descriptors.c
+ramstage-$(CONFIG_CHROMEOS) += chromeos.c
 
 subdirs-y += variants/baseboard