clk: qcom: Add support for gfx clock to ping pong PLLs

GFX3D clock source might require to ping pong between the available PLL
sources, so add support to check the current source and switch the next PLL
source for different frequency.

Change-Id: Iaf98e4d18fc0c3deb75ccce53e1c09cfc9dde550
Signed-off-by: Taniya Das <tdas@codeaurora.org>