common/Makefile: Add new symbol CONFIG_SPL_ENV_SUPPORT for environment in SPL

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: Ying Zhang <b40530@freescale.com>
Reviewed-by: Tom Rini <trini@ti.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>
diff --git a/README b/README
index 88274ed..e8359f8 100644
--- a/README
+++ b/README
@@ -3033,6 +3033,14 @@
 		CONFIG_SPL_LIBGENERIC_SUPPORT
 		Support for lib/libgeneric.o in SPL binary
 
+		CONFIG_SPL_ENV_SUPPORT
+		Support for the environment operating in SPL binary
+
+		CONFIG_SPL_NET_SUPPORT
+		Support for the net/libnet.o in SPL binary.
+		It conflicts with SPL env from storage medium specified by
+		CONFIG_ENV_IS_xxx but CONFIG_ENV_IS_NOWHERE
+
 		CONFIG_SPL_PAD_TO
 		Image offset to which the SPL should be padded before appending
 		the SPL payload. By default, this is defined as