env: Rename SYS_RELOC_GD_ENV_ADDR to ENV_RELOC_GD_ENV_ADDR

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.

Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
868 files changed