When booting using an SPL on am335x, if we want to support booting with
the boot ROM loader via USB (which uses RNDIS, making bootp and tftp
calls) we need to enable gadget eth in the SPL to load the main U-Boot
image. To enable CONFIG_SPL_ETH_SUPPORT, we must enable
CONFIG_SPL_ENV_SUPPORT as the environment is used by the eth support, but
we don't actually need to have environment variables saved in the SPL
environment. We do however have environment variables saved in the main
U-Boot image and enable CONFIG_ENV_OFFSET_REDUND (we are storing in raw
NAND). In such instances, even with the build config enabling both
CONFIG_CMD_SAVEENV and CONFIG_CMD_NAND, these options aren't set when
building the SPL, but CONFIG_ENV_OFFSET_REDUND still is.

Don't check this configuration option for SPL builds to enable the above
configuration.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>
Reviewed-by: Tom Rini <trini@konsulko.com>