drivers/spi/tpm: provide Kconfig to indicate CR50 usage

Going forward it's important to note when a CR50 is expected
to be present in the system. Additionally, this Kconfig addition
provides symmetry with the equivalent i2c Kconfig option.

BUG=b:35775104

Change-Id: Ifbd42b8a22f407534b23459713558c77cde6935d
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/18680
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins)
diff --git a/src/drivers/spi/tpm/Kconfig b/src/drivers/spi/tpm/Kconfig
index d66d9ff..8a4f3a3 100644
--- a/src/drivers/spi/tpm/Kconfig
+++ b/src/drivers/spi/tpm/Kconfig
@@ -11,3 +11,8 @@
 	int "Chip Select of the TPM chip on its SPI bus"
 	default 0
 	depends on SPI_TPM
+
+config MAINBOARD_HAS_SPI_TPM_CR50
+	bool
+	default n
+	depends on SPI_TPM
diff --git a/src/mainboard/google/gru/Kconfig b/src/mainboard/google/gru/Kconfig
index 3048b01..c9886f6 100644
--- a/src/mainboard/google/gru/Kconfig
+++ b/src/mainboard/google/gru/Kconfig
@@ -48,6 +48,7 @@
 config CHROMEOS
 	select EC_GOOGLE_CHROMEEC_SWITCHES
 	select EC_SOFTWARE_SYNC
+	select MAINBOARD_HAS_SPI_TPM_CR50 if GRU_HAS_TPM2
 	select SPI_TPM if GRU_HAS_TPM2
 	select VBOOT_VBNV_FLASH
 	select VIRTUAL_DEV_SWITCH