mb/google/myst: Enable PSP Verstage

Split the signed AMDFW binaries into their own section and enable PSP
verstage.

BUG=b:284984667
TEST=Build Myst BIOS image with PSP Verstage. Boot to OS successfully
with PSP verstage and a separate section for signed AMDFW binaries.

Change-Id: Ie0a54c157ebdebf9a0c95933c96865e0782a0f90
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/75703
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Martin Roth <martin.roth@amd.corp-partner.google.com>
diff --git a/src/mainboard/google/myst/Kconfig b/src/mainboard/google/myst/Kconfig
index 4bbfc20..0c7db6f 100644
--- a/src/mainboard/google/myst/Kconfig
+++ b/src/mainboard/google/myst/Kconfig
@@ -75,7 +75,15 @@
 	select EC_GOOGLE_CHROMEEC_SWITCHES
 	select VBOOT_LID_SWITCH
 	select VBOOT_SEPARATE_VERSTAGE
-	select VBOOT_STARTS_IN_BOOTBLOCK
+
+config VBOOT_STARTS_BEFORE_BOOTBLOCK
+	bool "Enable PSP_verstage"
+	default y if VBOOT
+	select SEPARATE_SIGNED_PSPFW
+
+config VBOOT_STARTS_IN_BOOTBLOCK
+	bool
+	default y if VBOOT && !VBOOT_STARTS_BEFORE_BOOTBLOCK
 
 # TODO(b/277087492): Enable GSC CBFS verification
 config VBOOT_GSCVD