hdmi-audio:mark the alsa ring buffer memory as uncached

hdmi-audio:mark the alsa ring buffer memory as uncached

BZ: 29792

When mmap method of driver is called, driver remaps
the buffers to user space using remap_pfn_range().
However this doesn't guaranteed to mark the pages
as non-cacheble.

As per Documentation/x86/pat.txt, if RAM region is
mmap'ed then in addition remap_pfn_range() we need to use
set_memory_uc() for marking pages as uncacheble.

Change-Id: I0152bb0cea1d0aef4b2eca9f82e59d932b1939a6
Signed-off-by: Ramesh Babu K V <ramesh.babu@intel.com>
Reviewed-on: http://android.intel.com:8080/42472
Reviewed-by: Abdullah, Omair M <omair.m.abdullah@intel.com>
Reviewed-by: Vinnakota, Lakshmi N <lakshmi.n.vinnakota@intel.com>
Reviewed-by: Gupta, ArvindX K <arvindx.k.gupta@intel.com>
Reviewed-by: Hibare, PramodX <pramodx.hibare@intel.com>
Tested-by: Hibare, PramodX <pramodx.hibare@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>