msm: clock-8960: Add 1.8MHz rate to 8064's gfx3d_clk plan

This rate will be used by the 'footswitch-8x60' driver when
controlling GFX3D power.

Change-Id: Ib796114dc90b468f1c0aa014a9db699f3b854adf
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>