drm/panel: sitronix: Use dev_ based logging

Standardize on the dev_ based logging and drop the include of drm_print.h.
Fix a few cases where "x@" was used when printing the mode.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Guido Günther <agx@sigxcpu.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200815125406.1153224-5-sam@ravnborg.org