msm: clock-local2: Clean up clk_ops_pixel

8974 and 8226 share the same clock ops on pixel clocks.
Therefore, move the set_rate_pixel and round_rate_pixel
into the common clock driver and remove the old unsupported
pixel clock ops.

Change-Id: I5b3867d41d97936c632ce1cdd1fb335ccea55399
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>