stm32mp1: disable OP-TEE reserved shared memory configuration in TF-A

Disables configuration of OP-TEE reserved shared memory in TF-A
configuration for STM32MP1 platform. This change prepares for a future
upgrade of TF-A release where this bootloader will deprecate configuration
of OP-TEE reserved shared memory for this platform [1] [2].

Link: https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/commit/?id=fb1d3bd9330ce70f735a344dd4223faffb261118 [1]
Link: https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/commit/?id=12e683a68049f6a3d0985a2cd1564e00115e809f [2]
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>
diff --git a/stm32mp1.mk b/stm32mp1.mk
index dd8f32a..d6a2ff4 100644
--- a/stm32mp1.mk
+++ b/stm32mp1.mk
@@ -124,6 +124,7 @@
 	AARCH32_SP=optee \
 	DEBUG=$(TFA_DEBUG) \
 	LOG_LEVEL=$(TFA_LOGLVL) \
+	STM32MP15_OPTEE_RSV_SHM=0 \
 	STM32MP_EMMC=1 STM32MP_SDMMC=1 \
 	STM32MP_RAW_NAND=0 STM32MP_SPI_NAND=0 STM32MP_SPI_NOR=0