stm32mp1: Move ENV_SIZE and ENV_OFFSET to Kconfig

Add arch stm32mp for ENV migration step and drop more
items from include/configs/xxx.h.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/arch/arm/mach-stm32mp/Kconfig b/arch/arm/mach-stm32mp/Kconfig
index 39a2a32..26dace10 100644
--- a/arch/arm/mach-stm32mp/Kconfig
+++ b/arch/arm/mach-stm32mp/Kconfig
@@ -26,6 +26,9 @@
 config SYS_MALLOC_LEN
 	default 0x2000000
 
+config ENV_SIZE
+	default 0x1000
+
 config TARGET_STM32MP1
 	bool "Support stm32mp1xx"
 	select ARCH_SUPPORT_PSCI if !STM32MP1_TRUSTED