Add support for environment in SPI flash

This is pretty incomplete...it doesn't handle reading the environment
before relocation, it doesn't support redundant environment, and it
doesn't support embedded environment. But apart from that, it does
seem to work.

Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
diff --git a/common/Makefile b/common/Makefile
index d90b5f2..b425795 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -113,6 +113,7 @@
 COBJS-y += env_flash.o
 COBJS-y += env_eeprom.o
 COBJS-y += env_onenand.o
+COBJS-y += env_sf.o
 COBJS-y += env_nvram.o
 COBJS-y += env_nowhere.o
 COBJS-y += exports.o