msm: kgsl: Don't bug if a VBIF implementation isn't enabled

As we get better at doing VBIF the number of registers we have to
program at init should be getting smaller and smaller - technically
converging on zero at some point.  Don't BUG_ON if a VBIF table
isn't defined for a particular platform because maybe we don't need
one?

Change-Id: Ic0dedbad25f779f50decb2df9e8ff4fa7f5f4c5f
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>