feat(stm32mp1): allow to override MTD base offset

Add an external parameter STM32MP_FORCE_MTD_START_OFFSET that allows to
override the default FIP offset used to read the first programmed image.
It can be used for NOR, RAW_NAND or SPI_NAND boot device.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Change-Id: Ibe664aae0e5ee90dd6629e544c9e034d751fffed
diff --git a/plat/st/stm32mp1/stm32mp1_fip_def.h b/plat/st/stm32mp1/stm32mp1_fip_def.h
index 82e53db..5652597 100644
--- a/plat/st/stm32mp1/stm32mp1_fip_def.h
+++ b/plat/st/stm32mp1/stm32mp1_fip_def.h
@@ -106,7 +106,11 @@
  * STM32MP1 RAW partition offset for devices without GPT
  ******************************************************************************/
 #define STM32MP_EMMC_BOOT_FIP_OFFSET	U(0x00040000)
+#ifndef STM32MP_NOR_FIP_OFFSET
 #define STM32MP_NOR_FIP_OFFSET		U(0x00080000)
+#endif
+#ifndef STM32MP_NAND_FIP_OFFSET
 #define STM32MP_NAND_FIP_OFFSET		U(0x00200000)
+#endif
 
 #endif /* STM32MP1_FIP_DEF_H */