Rename the variable and add ENV_ prefix, so that all configuration
options which are related to environment would have an CONFIG_ENV_
prefix. No functional change.
Use ENV_MMC_SW_PARTITION to clarify this is the SD/MMC software
partition table entry selector. Update the help text accordingly.
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
ffc4914703