msm: kgsl: Restrict GPU virtual address when using CFF

If CFF is enabled then the GPU virtual address range needs
to be restricted to 512MB. This is a requirement of the virtual
platform on which the CFF vectors are replayed.

Change-Id: I77663edee942c26206e4a058f2bf47369e2348e6
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>