stm32mp1: move CONFIG_ENV in Kconfig

Move 2 ENV configuration flags in board Kconfig
- CONFIG_ENV_SECT_SIZE
- CONFIG_ENV_OFFSET

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/board/st/stm32mp1/Kconfig b/board/st/stm32mp1/Kconfig
index 5ab9415..5f81f94 100644
--- a/board/st/stm32mp1/Kconfig
+++ b/board/st/stm32mp1/Kconfig
@@ -9,4 +9,10 @@
 config SYS_CONFIG_NAME
 	default "stm32mp1"
 
+config ENV_SECT_SIZE
+	default 0x40000 if ENV_IS_IN_SPI_FLASH
+
+config ENV_OFFSET
+	default 0x280000 if ENV_IS_IN_SPI_FLASH
+
 endif