dclk_lcdc can be sourced from a general pll source as well
as the hdmiphy's pll output. We will want to set this source
by hand (to the system-pll-source in most cases) and also
want rate changes to this clock to be able to also touch
the pll source clock if needed, so add CLK_SET_RATE_PARENT
and CLK_SET_RATE_NO_REPARENT for dclk_lcdc.