imx: ventana: Rework CONFIG_CMD_EECONFIG code to not be included in SPL

The command can only be used from full U-Boot, so do not build it into
SPL.

Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Acked-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>