board: st: add generic board for STM32MP1 family

Add first support for STM32MP157C-ED1 board with "Basic" boot chain
1/ Boot Rom: load SPL with STM32 image header in SYSRAM
2/ SPL: power up and initialize the DDR and load U-Boot image
        from SDCARD in DDR
3/ U-Boot: search and load extlinux.conf in SDCARD
           (DISTRO activated)

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/arch/arm/mach-stm32mp/Kconfig b/arch/arm/mach-stm32mp/Kconfig
index ab94879..8c755f8 100644
--- a/arch/arm/mach-stm32mp/Kconfig
+++ b/arch/arm/mach-stm32mp/Kconfig
@@ -38,4 +38,6 @@
 		when DDR driver is used:
 		  DDR + 1MB (0xC0100000)
 
+source "board/st/stm32mp1/Kconfig"
+
 endif