drm: sun4i: rename sun4i_dotclock to sun4i_tcon_dclk

While the rate of TCON0's DCLK matches dotclock for parallel and LVDS
outputs, this doesn't hold for DSI. The 'D' in DCLK actually stands for
'Data' according to Allwinner's manuals. The clock is mostly referred to
as dclk throughout this driver already anyway, so stick with that.

Signed-off-by: Roman Beranek <me@crly.cz>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20230505052110.67514-4-me@crly.cz