spi_flash: Move spi flash opcodes to spi_flash.h

BUG=chrome-os-partner:59832
BRANCH=None
TEST=Compiles successfully

Change-Id: I3b6656923bb312de470da43a23f66f350e1cebc7
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/17680
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/baytrail/spi.c

@@ -21,6 +21,7 @@
 #include <arch/io.h>
 #include <console/console.h>
 #include <device/pci_ids.h>
+#include <spi_flash.h>
 #include <spi-generic.h>
 
 #include <soc/lpc.h>