msm: kgsl: Added DRM_IOCTL_KGSL_GEM_GET_ION_FD ioctl to DRM device.

To allow for user space ion based zero copy operations
(such as camera preview) on X11 allocated buffers (e.g. Pixmaps).
This ioctl returns a sharable ION file descriptor given a GEM object.

Change-Id: I055712b8fa469c99a224933a1f2fd62d2d811536
Signed-off-by: Michael Street <mstreet@codeaurora.org>