nand.h: Cleanup linux/mtd/rawnand.h usage

We only include <linux/mtd/rawnand.h> in <nand.h> for the forward
declaration of struct nand_chip, so do that directly.  Then, include
<linux/mtd/rawnand.h> where required directly.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/socrates/nand.c b/board/socrates/nand.c
index 07c4936..9b7ffee 100644
--- a/board/socrates/nand.c
+++ b/board/socrates/nand.c
@@ -9,6 +9,7 @@
 #if defined(CONFIG_SYS_NAND_BASE)
 #include <nand.h>
 #include <linux/errno.h>
+#include <linux/mtd/rawnand.h>
 #include <asm/io.h>
 
 static int state;