sf: Add memory mapped read support

Qspi controller can have a memory mapped port which can be used for
data read. Added support to enable memory mapped port read.

This patch enables the following:
- It enables exchange of memory map address between mtd and qspi
through the introduction of "memory_map" flag.
- Add support to communicate to the driver that memory mapped
 transfer is to be started through introduction of new flags like
"SPI_XFER_MEM_MAP" and "SPI_XFER_MEM_MAP_END".

This will enable the spi controller to do memory mapped configurations
if required.

Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
diff --git a/drivers/mtd/spi/sf_ops.c b/drivers/mtd/spi/sf_ops.c
index c009af5..2396e22 100644
--- a/drivers/mtd/spi/sf_ops.c
+++ b/drivers/mtd/spi/sf_ops.c
@@ -269,7 +269,9 @@
 
 	/* Handle memory-mapped SPI */
 	if (flash->memory_map) {
+		spi_xfer(flash->spi, 0, NULL, NULL, SPI_XFER_MMAP);
 		memcpy(data, flash->memory_map + offset, len);
+		spi_xfer(flash->spi, 0, NULL, NULL, SPI_XFER_MMAP_END);
 		return 0;
 	}