intel/common/block/fast_spi: Add config option to disable write status

Chrome OS systems rely on the write status register to enable/disable
flash write protection and disabling this opcode breaks the ability
to enable or disable write protection with flashrom.

Add a configure option for this feature that will disable the opcode
for Write Status commands unless CONFIG_CHROMEOS is enabled.

Tested to ensure that a default build without CONFIG_CHROMEOS has this
option enabled while a build with CONFIG_CHROMEOS does not.  Also
ensured that when this option is disabled (for Chrome OS) then flashrom
can be used with the --wp-enable and --wp-disable commands, depending
on the state of the external write protect pin.

Change-Id: Ia2ef3c3b1e10fba2c437e083f3537022f1fce84a
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/21021
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
diff --git a/src/soc/intel/common/block/fast_spi/fast_spi.c b/src/soc/intel/common/block/fast_spi/fast_spi.c
index fe0217a..f7ef685 100644
--- a/src/soc/intel/common/block/fast_spi/fast_spi.c
+++ b/src/soc/intel/common/block/fast_spi/fast_spi.c
@@ -144,7 +144,10 @@
 void fast_spi_lock_bar(void)
 {
 	void *spibar = fast_spi_get_bar();
-	const uint16_t hsfs = SPIBAR_HSFSTS_FLOCKDN | SPIBAR_HSFSTS_WRSDIS;
+	uint16_t hsfs = SPIBAR_HSFSTS_FLOCKDN;
+
+	if (IS_ENABLED(CONFIG_FAST_SPI_DISABLE_WRITE_STATUS))
+		hsfs |= SPIBAR_HSFSTS_WRSDIS;
 
 	write16(spibar + SPIBAR_HSFSTS_CTL, hsfs);
 }