env: mmc: statically set the environment partition name

The new opt-out setting, CONFIG_ENV_MMC_PARTITION, statically sets
the MMC environment partition name. Prior to this patch, the only way
to declare this partition name was by creating a
'u-boot,mmc-env-partition' parameter in the device-tree's /config node.

This setting provides additional flexibility, particularly in cases
where accessing the device-tree is not straightforward (e.g. QEMU).

If undeclared, the device-tree's setting will be used.

Signed-off-by: Emmanuel Di Fede <emmanuel.difede@cysec.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/env/Kconfig b/env/Kconfig
index 7342397..13e3210 100644
--- a/env/Kconfig
+++ b/env/Kconfig
@@ -662,6 +662,18 @@
 	  partition 0 or the first boot partition, which is 1 or some other defined
 	  partition.
 
+config USE_ENV_MMC_PARTITION
+	bool "use the mmc environment partition name"
+	depends on ENV_IS_IN_MMC
+
+config ENV_MMC_PARTITION
+	string "mmc environment partition name"
+	depends on USE_ENV_MMC_PARTITION
+	help
+	  MMC partition name used to save environment variables.
+	  If this variable is unset, u-boot will try to get the env partition name
+	  from the device-tree's /config node.
+
 config ENV_MMC_USE_DT
 	bool "Read partition name and offset in DT"
 	depends on ENV_IS_IN_MMC && OF_CONTROL