msm: kgsl: Reorganize perfcounter code

Move perfcounter functions init, save, restore, close, write and other
perfcounter related functions to a common file. This keeps all perfcounter
related code in one file -> better readability, increases the common
code and reduces the number of function pointers to implement for new
GPU cores.

Change-Id: I30b128e6876871e82486fb2e39ebacc0a846ed6c
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>