msm: kgsl: Add support for multiple bus scaling tables

It's possible that a target may have more than one bus
scaling table based on types of DDR that are supported.
In such a scenario we need to create a device node for
each table.

Change-Id: If5bfd4fee373625fca76d5cc060d4ecc274566ce
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>