mb/hp/z220_series: Enable VBOOT_VBNV_FLASH

To deprecate VBOOT_VBNV_CMOS [1], replace VBOOT_VBNV_CMOS with
VBOOT_VBNV_FLASH for z220_series.

[1] https://web.archive.org/web/20230115020833/https://issuetracker.google.com/issues/235293589?pli=1

BUG=b:235293589
TEST=./util/abuild/abuild -t HP_Z220_CMT_WORKSTATION -a \
     # with VBOOT enabled and a custom FMDFILE with RW_NVRAM region

Change-Id: I1c60a44fb12fd093f45cf54ef2f9e0e02afc80bd
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/72891
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yidi Lin <yidilin@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
diff --git a/src/mainboard/hp/z220_series/Kconfig b/src/mainboard/hp/z220_series/Kconfig
index 1be3972..76c114c 100644
--- a/src/mainboard/hp/z220_series/Kconfig
+++ b/src/mainboard/hp/z220_series/Kconfig
@@ -27,17 +27,13 @@
 if BOARD_HP_Z220_SERIES_COMMON
 
 config VBOOT
-	select VBOOT_VBNV_CMOS
+	select VBOOT_VBNV_FLASH
 	select VBOOT_NO_BOARD_SUPPORT
 	select GBB_FLAG_DISABLE_LID_SHUTDOWN
 	select GBB_FLAG_DISABLE_PD_SOFTWARE_SYNC
 	select GBB_FLAG_DISABLE_EC_SOFTWARE_SYNC
 	select GBB_FLAG_DISABLE_FWMP
 
-config VBOOT_VBNV_OFFSET
-	hex
-	default 0x2a
-
 config CBFS_SIZE
 	default 0x570000