nb/intel/broadwell: Add an option for where verstage starts

Previously broadwell used a romcc bootblock and starting verstage in
romstage was madatory but with C_ENVIRONMENT_BOOTBLOCK it is also
possible to have a separate verstage.

This selects using a separate verstage by default but still keeps the
option around to use verstage in romstage.

With a separate verstage the romstage becomes an RW stage.
The mrc.bin however is only added to the RO COREBOOT fmap region as it
requires to be run at a specific offset. This means that coreboot will
have to jump from a RW region to the RO region for that binary and
back to that RW region after that binary is done initializing the
memory.

Change-Id: I900233cadb3c76da329fb98f93917570e633365f
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/30384
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/soc/intel/broadwell/Kconfig b/src/soc/intel/broadwell/Kconfig
index 9dd2f4f..b685391 100644
--- a/src/soc/intel/broadwell/Kconfig
+++ b/src/soc/intel/broadwell/Kconfig
@@ -67,9 +67,25 @@
 	bool
 	default y
 
+config BROADWELL_VBOOT_IN_BOOTBLOCK
+	depends on VBOOT
+	bool "Start verstage in bootblock"
+	default y
+	select VBOOT_STARTS_IN_BOOTBLOCK
+	select VBOOT_SEPARATE_VERSTAGE
+	help
+	  Broadwell can either start verstage in a separate stage
+	  right after the bootblock has run or it can start it
+	  after romstage for compatibility reasons.
+	  Broadwell however uses a mrc.bin to initialse memory which
+	  needs to be located at a fixed offset. Therefore even with
+	  a separate verstage starting after the bootblock that same
+	  binary is used meaning a jump is made from RW to the RO region
+	  and back to the RW region after the binary is done.
+
 config VBOOT
 	select VBOOT_MUST_REQUEST_DISPLAY
-	select VBOOT_STARTS_IN_ROMSTAGE
+	select VBOOT_STARTS_IN_ROMSTAGE if !BROADWELL_VBOOT_IN_BOOTBLOCK
 
 config MMCONF_BASE_ADDRESS
 	hex
@@ -141,6 +157,13 @@
 	hex
 	default 0xfffa0000
 
+# The UEFI System Agent binary needs to be at a fixed offset in the flash
+# and can therefore only reside in the COREBOOT fmap region
+config RO_REGION_ONLY
+	string
+	depends on VBOOT
+	default "mrc.bin"
+
 endif # HAVE_MRC
 
 config PRE_GRAPHICS_DELAY