msm: kgsl: Add NOP name to postmortem dump

There are several different NOP commands placed in the ringbuffer
for book keeping.  Rather than just print the random tag associated
with the NOP, print a meaningful string.

Change-Id: Id21743b598047b1b3ff06580ad206cf3e675c83d
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>