msm: kgsl: Standardize ringbuffers in the snapshot

'start' and 'stop' in the snapshot ringbuffer header are supposed to
be the dword offset that the data starts and stops at respectively.
For the current ringbuffer which is parsed 'start' and 'stop' are
equal to the CP wptr but all other ringbuffers are just dumped from
start to finish so 'start' and stop' should be 0 and KGSL_RB_DWORDS.
And having said that, why are we bothering to make the current
ringbuffer special anyway? In every case we are dumping the entire
ringbuffer so we might as well dump it in order. While messing about
in this code go a few more steps to make sure that we don't dump the
same ringbuffer more than once.

Change-Id: Ic0dedbada33adda660b7f0bf5eb165b0aa159004
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>