msm: kgsl: Dump debugbus data in gmu snapshot

Debugbus data can be accessed even if the gx headswitch or
sptprac is off. For example, the gmu cx debugbus data can be
captured to aid in debugging. Debug bus data of rest of the
GPU blocks will show as 0x5c00bd00 if gx headswitch is off.

Change-Id: Ifb5ab5cbd55676b46af571b3c19f52a42e7db806
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>