msm: kgsl: Remove struct kgsl_device_platform_data

The platform data is from a pre DT era and adds an additional global
header that we don't need to deal with. Put it out to pasture.

Change-Id: Ic0dedbad1bbda06380dfa5f6193a4445b3caf24c
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>