sf: Add flag status register polling support

Flag status register polling is required for micron 512Mb flash
devices onwards, for performing erase/program operations.

Like polling for WIP(Write-In-Progress) bit in read status register,
spi_flash_cmd_wait_ready will poll for PEC(Program-Erase-Control)
bit in flag status register.

Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/spi_flash.h b/include/spi_flash.h
index e22d698..e80785f 100644
--- a/include/spi_flash.h
+++ b/include/spi_flash.h
@@ -46,6 +46,9 @@
 	/* Current flash bank */
 	u8		bank_curr;
 #endif
+	/* Poll cmd - for flash erase/program */
+	u8		poll_cmd;
+
 	void *memory_map;	/* Address of read-only SPI flash access */
 	int		(*read)(struct spi_flash *flash, u32 offset,
 				size_t len, void *buf);