common: Drop flash.h from common header

Move this uncommon header out of the common header.

Fix up some style problems in flash.h while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mtd/spi/sf_dataflash.c b/drivers/mtd/spi/sf_dataflash.c
index 55fb4bd..b1a3804 100644
--- a/drivers/mtd/spi/sf_dataflash.c
+++ b/drivers/mtd/spi/sf_dataflash.c
@@ -10,6 +10,7 @@
 #include <dm.h>
 #include <errno.h>
 #include <fdtdec.h>
+#include <flash.h>
 #include <spi.h>
 #include <spi_flash.h>
 #include <div64.h>