drm/msm: Get rid of the REG_ADRENO offsets

As newer GPU families are added it makes less sense to maintain a
"generic" version functions for older families. Move adreno_submit()
and get_rptr() into the target specific code for a2xx, a3xx and a4xx.
Add a parameter to adreno_flush to pass the target specific WPTR register
instead of relying on the generic register.

All of this gets rid of the last of the REG_ADRENO offsets so remove all
all the register definitions and infrastructure.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>