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/stm32_flash.c b/drivers/mtd/stm32_flash.c
index fd0d550..95afa2d 100644
--- a/drivers/mtd/stm32_flash.c
+++ b/drivers/mtd/stm32_flash.c
@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <flash.h>
 #include <asm/io.h>
 #include <asm/arch/stm32.h>
 #include "stm32_flash.h"