drivers/spi: Allow SoC to provide the SPI flash CS index

On AMD platforms the PSP can boot from different SPI CS lines
and do a recovery boot in case the default CS0 isn't usable.

Allow the SoC to provide the current boot_device CS line by
adding a new weak function.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Maximilian Brune <maximilian.brune@9elements.com>
Change-Id: Ic9ed54b7979405d433f22458265f09701cda842e
Reviewed-on: https://review.coreboot.org/c/coreboot/+/90777
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/drivers/spi/boot_device_rw_nommap.c

@@ -8,6 +8,11 @@
 static struct spi_flash sfg;
 static bool sfg_init_done;
 
+__weak int boot_device_spi_cs(void)
+{
+	return 0;	/* Default to chip select 0 */
+}
+
 static ssize_t spi_readat(const struct region_device *rd, void *b,
 				size_t offset, size_t size)
 {
@@ -47,7 +52,7 @@ static const struct region_device spi_rw =
 static void boot_device_rw_init(void)
 {
 	const int bus = CONFIG_BOOT_DEVICE_SPI_FLASH_BUS;
-	const int cs = 0;
+	const int cs = boot_device_spi_cs();
 
 	if (sfg_init_done == true)
 		return;

src/drivers/spi/cbfs_spi.c

@@ -17,6 +17,11 @@
 static struct spi_flash spi_flash_info;
 static bool spi_flash_init_done;
 
+__weak int boot_device_spi_cs(void)
+{
+	return 0;	/* Default to chip select 0 */
+}
+
 /*
  * SPI speed logging for big transfers available with BIOS_DEBUG. The format is:
  *
@@ -82,7 +87,7 @@ static struct mmap_helper_region_device mdev =
 void boot_device_init(void)
 {
 	int bus = CONFIG_BOOT_DEVICE_SPI_FLASH_BUS;
-	int cs = 0;
+	int cs = boot_device_spi_cs();
 
 	if (spi_flash_init_done == true)
 		return;

src/include/boot_device.h

@@ -27,6 +27,9 @@ enum bootdev_prot_type {
  * most likely not to work so don't rely on such semantics.
  */
 
+/* Return the chip select index used for probing the SPI flash. */
+int boot_device_spi_cs(void);
+
 /* Return the region_device for the read-only boot device. This is the root
    device for all CBFS boot devices. */
 const struct region_device *boot_device_ro(void);