msm: kgsl: Remove code for unsupported a3xx targets

Some time a very long time ago many of the a3xx targets were removed
from the GPU list but the target specific code wasn't removed.

Change-Id: Ic0dedbad2dc2c587014f13e639d56068718f6625
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>