common: Drop net.h from common header

Move this header out of the common header. Network support is used in
quite a few places but it still does not warrant blanket inclusion.

Note that this net.h header itself has quite a lot in it. It could be
split into the driver-mode support, functions, structures, checksumming,
etc.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mmc/dw_mmc.c b/drivers/mmc/dw_mmc.c
index 1224540..6290b7f 100644
--- a/drivers/mmc/dw_mmc.c
+++ b/drivers/mmc/dw_mmc.c
@@ -14,6 +14,7 @@
 #include <mmc.h>
 #include <dwmmc.h>
 #include <wait_bit.h>
+#include <asm/cache.h>
 #include <power/regulator.h>
 
 #define PAGE_SIZE 4096