msm: kgsl: Add a property to query gpu speed bin

usermode driver can query speed bin value
to modify settings based on speed bin. Add
support to for new gpu speed bin property.

Change-Id: I99323e7861e5674441d8f94ce7f2be604340c5f1
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>