mali_kbase: Move all RT threads onto a coremask

Updates all lightweight realtime worker threads in kbase to use
a coremask that limits them to the little cluster. Created a
single function that performs this set up and moved all rt thread
creation instances to use it.

Bug: 181777616
Bug: 181582516
Signed-off-by: Sidath Senanayake <sidaths@google.com>
Change-Id: Ib499541aa7a5777f3b9327637f862c6c67fa2fa0