msm: kgsl: Re-enable performance counters

Commit c3a73b6c accidently disabled
all performance counters which caused the fault tolerance to falsely
trigger more often.  Re-enable the performance counters and remove
duplicate code to enable the VBIF registers (they are enabled by the
a3xx_perfcounter_enable function).

CRs-fixed: 581430
Change-Id: Ic0dedbad277e796e6b2e7bd8e938cb8afe03207b
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>