stm32mp1: define STM32MP15C-ED1

STM32MP15C-ED1 is the child board plugged on EV1 mother board. ED1 can
be used without its mother board with some interface restrictions
(I.e. no USB-C). This change defines the platform flavor. The several
components (optee_os, tf-a, u-boot, linux) already support ED1 DTS file
identifier.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@st.com>
Acked-by: Jerome Forissier <jerome@forissier.org>
diff --git a/stm32mp1.mk b/stm32mp1.mk
index 193230e..7995ef8 100644
--- a/stm32mp1.mk
+++ b/stm32mp1.mk
@@ -22,6 +22,9 @@
 else ifeq ($(PLATFORM),stm32mp1-157C_EV1)
 BREXT_FLAVOR		= STM32MP157C-EV1
 STM32MP1_DTS_BASENAME	= stm32mp157c-ev1
+else ifeq ($(PLATFORM),stm32mp1-157C_ED1)
+BREXT_FLAVOR		= STM32MP157C-ED1
+STM32MP1_DTS_BASENAME	= stm32mp157c-ed1
 else
 $(error Unknown PLATFORM $(PLATFORM))
 endif