msm: kgsl: Change struct pointers to void pointers

Change struct kgsl_ibdesc and kgsl_cmd_syncpoint pointers to void
pointers since we cast them to void __user * anyway. Also, this
enables us to pass pointers to structs other than the above two.

Change-Id: Idc3464b049dfdff51ecd0c32a47d4f5d3b0e4980
Signed-off-by: Shrenuj Bansal <shrenujb@codeaurora.org>