x86, pat: workaround to force PAT usage

x86, pat: workaround to force PAT usage

When run under haxm certain CPU features appear inaccesible from guest
and at the moment there seems to be no proper way to set them up from the
host side. The patch allows to forcefully enable x86 Page Attribute
Table and therefore use different memory caching policies at the page
level granularity. PAT significantly improves performance when mmaped
device buffers are accessed.

WARNING: once a proper solution is figured out for haxm case the patch
should be reverted. Currently it is more like a hack to avoid terrible
performance on certain scenarios like decoding high resolution video
directly into the mmaped video buffer.

Change-Id: Ib626a93b2ff16cc8bbdee186cfe67cff6b29e618
Signed-off-by: Vasiliy Ulyanov <v.ulyanov@samsung.com>
Signed-off-by: Sooyoung Ha <yoosah.ha@samsung.com>