tpm: st33zp24: Add tpm st33zp24 spi support

Add support for TPM ST33ZP24 spi.

The ST33ZP24 does have a spi interface.
The transport protocol is proprietary.

For spi we are relying only on DM_SPI.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
diff --git a/README b/README
index ec73a4e..c7c9e0a 100644
--- a/README
+++ b/README
@@ -1430,6 +1430,10 @@
 			Support for STMicroelectronics ST33ZP24 I2C devices.
 			Requires TPM_ST33ZP24 and I2C.
 
+			CONFIG_TPM_ST33ZP24_SPI
+			Support for STMicroelectronics ST33ZP24 SPI devices.
+			Requires TPM_ST33ZP24 and SPI.
+
 		CONFIG_TPM_ATMEL_TWI
 		Support for Atmel TWI TPM device. Requires I2C support.