board: stm32mp1: move CONFIG_ENV_XXX in defconfig

Move CONFIG_ENV_SECT_SIZE and CONFIG_ENV_OFFSET in stm32mp15_*_defconfig
for ST board with NOR support (STM32MP15xx-EV1 boards)
- CONFIG_SECT_SIZE values = the max supported NOR erase size (256KB)
- CONFIG_ENV_OFFSET = offset for NOR (ENV_IS_IN_SPI_FLASH)

This Patch prepares the U-Boot support of boards with STM32MP15x SOC
not provided by STMicroelectronics.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/configs/stm32mp15_basic_defconfig b/configs/stm32mp15_basic_defconfig
index c85369c..1061d38 100644
--- a/configs/stm32mp15_basic_defconfig
+++ b/configs/stm32mp15_basic_defconfig
@@ -1,6 +1,8 @@
 CONFIG_ARM=y
 CONFIG_ARCH_STM32MP=y
 CONFIG_SYS_MALLOC_F_LEN=0x3000
+CONFIG_ENV_SECT_SIZE=0x40000
+CONFIG_ENV_OFFSET=0x280000
 CONFIG_SPL_MMC_SUPPORT=y
 CONFIG_SPL=y
 CONFIG_TARGET_STM32MP1=y