fsp_broadwell_de: Enable early write access to the SPI flash

If VBOOT is used on a mainboard based on fsp_broadwell_de then VBOOT
needs to be able to write to its NV data which may be stored on the SPI
flash. Enable write access to the SPI flash on SoC level. If the
mainboard does not use VBOOT the linker will drop the extra code. The
benefit is that this code is at least compiled and therefore build
tested with fsp_broadwell_de.

Change-Id: I90a2d30f5749c75df2b286dce6779f10dde62632
Signed-off-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35598
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/soc/intel/fsp_broadwell_de/Kconfig

@@ -29,6 +29,8 @@ config CPU_SPECIFIC_OPTIONS
 	select SOC_INTEL_COMMON
 	select SOC_INTEL_COMMON_BLOCK
 	select SOC_INTEL_COMMON_BLOCK_IMC
+	select BOOT_DEVICE_SUPPORTS_WRITES
+	select BOOT_DEVICE_SPI_FLASH_RW_NOMMAP_EARLY
 
 config VBOOT
 	select VBOOT_STARTS_IN_ROMSTAGE