driver: Add support of image load for MMC & SPI in SPL

Add support of loading image, binary for MMC and SPI during SPL boot.

Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>
diff --git a/include/spi_flash.h b/include/spi_flash.h
index 1a11286..2db53c7 100644
--- a/include/spi_flash.h
+++ b/include/spi_flash.h
@@ -158,5 +158,6 @@
 }
 
 void spi_boot(void) __noreturn;
+void spi_spl_load_image(uint32_t offs, unsigned int size, void *vdst);
 
 #endif /* _SPI_FLASH_H_ */