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>

Documentation/devicetree/bindings/sram/sram.txt

@@ -25,6 +25,11 @@ Required properties in the sram node:
 - ranges : standard definition, should translate from local addresses
            within the sram to bus addresses
 
+Optional properties in the sram node:
+
+- no-memory-wc : the flag indicating, that SRAM memory region has not to
+                 be remapped as write combining. WC is used by default.
+
 Required properties in the area nodes:
 
 - reg : iomem address range, relative to the SRAM range