There will need the environment in SPL for reasons other than network
support (in particular, hwconfig contains info for how to set up DDR).

Add a new symbol CONFIG_SPL_ENV_SUPPORT to replace CONFIG_SPL_NET_SUPPORT
for environment in common/Makefile.
Signed-off-by: NYing Zhang <b40530@freescale.com>
Reviewed-by: NTom Rini <trini@ti.com>
Signed-off-by: NAndy Fleming <afleming@freescale.com>