spi_master: Introduce SPI_MASTER_4BA feature flag

Add a feature flag SPI_MASTER_4BA to `struct spi_master` that advertises
programmer-side support for 4-byte addresses in generic commands (and
read/write commands if the master uses the default implementations). Set
it for all masters that handle commands address-agnostic.

Don't prefer native 4BA instructions if the master doesn't support them.

Change-Id: Ife66e3fc49b9716f9c99cad957095b528135ec2c
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/22421
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
diff --git a/buspirate_spi.c b/buspirate_spi.c
index b6554ac..6f4c6d0 100644
--- a/buspirate_spi.c
+++ b/buspirate_spi.c
@@ -136,6 +136,7 @@
 
 static struct spi_master spi_master_buspirate = {
 	.type		= SPI_CONTROLLER_BUSPIRATE,
+	.features	= SPI_MASTER_4BA,
 	.max_data_read	= MAX_DATA_UNSPECIFIED,
 	.max_data_write	= MAX_DATA_UNSPECIFIED,
 	.command	= NULL,