mtd: cfi: Add support for status register polling

The status register is optional in the AMD command sets, but it's
presence can be checked by reading out CFI table entry 0xc bit 0.
If the register is present, prefer using it's bit 7 to determine
if the flash is busy over reading the flash ; this is needed ie.
on Hyperflash memories.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/include/mtd/cfi_flash.h b/include/mtd/cfi_flash.h
index eade2b3..095725a 100644
--- a/include/mtd/cfi_flash.h
+++ b/include/mtd/cfi_flash.h
@@ -62,6 +62,7 @@
 
 #define FLASH_OFFSET_MANUFACTURER_ID	0x00
 #define FLASH_OFFSET_DEVICE_ID		0x01
+#define FLASH_OFFSET_LOWER_SW_BITS	0x0C
 #define FLASH_OFFSET_DEVICE_ID2		0x0E
 #define FLASH_OFFSET_DEVICE_ID3		0x0F
 #define FLASH_OFFSET_CFI		0x55