msm: kgsl: Add kgsl_malloc/kgsl_free helpers

Instead of constantly trying to reinvent the wheel when doing
kernel allocations of indeterminate size create a alloc/free
pair of functions that can do the magic for us. Replace all of
the existing bits and pieces with the new function calls.

Change-Id: Ic0dedbad349ce1196899f4c24a374e0bfed3a923
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>