msm: kgsl: Get rid of GSL_RB_WRITE

The use of GSL_RB_WRITE involves a bunch of hand wringing and
extra variables to get right.  adreno_ringbuffer_allocspace()
and adreno_ringbuffer_submit() know almost all the important
information anyway so move the functionality into those two
functions.

Change-Id: Ic0dedbadb8cebb18e4808b841620a3faa900fd3f
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>