misc: sram: add optional ioremap without write combining

Some SRAM users may require non-bufferable access to the memory, which is
impossible, because devm_ioremap_wc() is used for setting sram->virt_base.

This commit adds optional flag 'no-memory-wc', which allow to choose remap
method, using DT property. Documentation is updated accordingly.

Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/misc/sram.c b/drivers/misc/sram.c
index 736dae7..69cdabe 100644
--- a/drivers/misc/sram.c
+++ b/drivers/misc/sram.c
@@ -360,7 +360,10 @@
 		return -EBUSY;
 	}
 
-	sram->virt_base = devm_ioremap_wc(sram->dev, res->start, size);
+	if (of_property_read_bool(pdev->dev.of_node, "no-memory-wc"))
+		sram->virt_base = devm_ioremap(sram->dev, res->start, size);
+	else
+		sram->virt_base = devm_ioremap_wc(sram->dev, res->start, size);
 	if (IS_ERR(sram->virt_base))
 		return PTR_ERR(sram->virt_base);