Enable VBOOT_VBNV_FLASH for SOC_INTEL_BRASWELL

To deprecate VBOOT_VBNV_CMOS [1], replace VBOOT_VBNV_CMOS with
VBOOT_VBNV_FLASH for boards using SOC_INTEL_BRASWELL.

Currently BOOT_DEVICE_SPI_FLASH_NO_EARLY_WRITES is selected for
CPU_INTEL_HASWELL, SOC_INTEL_BRASWELL and others (see [2]). However,
there seems to be no particular reason on those platforms. We've dropped
the config for haswell. Now do the same for SOC_INTEL_BRASWELL, so that
VBOOT_VBNV_FLASH can be enabled.

VBOOT_VBNV_FLASH is enabled for the following boards:

- facebook/fbg1701: A 0x2000 RW_NVRAM region is allocated, with the
  FW_MAIN_A(CBFS) size reduced by 0x2000.
- google/cyan, intel/strago: Repurpose RW_UNUSED as RW_NVRAM.

[1] https://issuetracker.google.com/issues/235293589
[2] commit 6c2568f4f5
    ("drivers/spi: Add BOOT_DEVICE_SPI_FLASH_NO_EARLY_WRITES config")

BUG=b:235293589
TEST=./util/abuild/abuild -t FACEBOOK_FBG1701 -a (with VBOOT selected)
TEST=./util/abuild/abuild -x -t GOOGLE_CYAN -a
TEST=./util/abuild/abuild -x -t INTEL_STRAGO -a

Change-Id: I46542c2887b254f59245f20b8642b023a7871708
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/71544
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Frans Hendriks <fhendriks@eltan.com>
Reviewed-by: Erik van den Bogaert <ebogaert@eltan.com>

src/soc/intel/braswell/Kconfig

@@ -9,7 +9,6 @@ config CPU_SPECIFIC_OPTIONS
 	def_bool y
 	select ACPI_INTEL_HARDWARE_SLEEP_VALUES
 	select ARCH_X86
-	select BOOT_DEVICE_SPI_FLASH_NO_EARLY_WRITES
 	select BOOT_DEVICE_SUPPORTS_WRITES
 	select CACHE_MRC_SETTINGS
 	select SUPPORT_CPU_UCODE_IN_CBFS