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/linux_spi.c b/linux_spi.c
index 611559a..1d3605a 100644
--- a/linux_spi.c
+++ b/linux_spi.c
@@ -57,6 +57,7 @@
 
 static const struct spi_master spi_master_linux = {
 	.type		= SPI_CONTROLLER_LINUX,
+	.features	= SPI_MASTER_4BA,
 	.max_data_read	= MAX_DATA_UNSPECIFIED, /* TODO? */
 	.max_data_write	= MAX_DATA_UNSPECIFIED, /* TODO? */
 	.command	= linux_spi_send_command,