sf: Enable swaprect optimization by default only on QCOMs

 * This is confirmed to cause problems at least on i9500.
 * Only enable it by default on QCOMs, other devices can opt
   in using the system property.

Change-Id: Ic00137201f4a5383877f4033473c1ea5ac32a3a7
Merge pull request #17 from CyanogenMod/cm-11.0

sf: Enable swaprect optimization by default only on QCOMs