drm/mcde: Support DPI output

This implements support for DPI output using the port node
in the device tree to connect a DPI LCD display to the
MCDE. The block also supports TV-out but we leave that
for another day when we have a hardware using it.

We implement parsing and handling of the "port" node,
and follow that to the DPI endpoint.

The clock divider used by the MCDE to divide down the
"lcdclk" (this has been designed for TV-like frequencies)
is represented by an ordinary clock provider internally
in the MCDE. This idea was inspired by the PL111 solution
by Eric Anholt: the divider also works very similar to
the Pl111 clock divider.

We take care to clear up some errors regarding the number
of available formatters and their type. We have 6 DSI
formatters and 2 DPI formatters.

Tested on the Samsung GT-I9070 Janice mobile phone.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Stephan Gerhold <stephan@gerhold.net>
Cc: phone-devel@vger.kernel.org
Cc: upstreaming@lists.sr.ht
Link: https://patchwork.freedesktop.org/patch/msgid/20201112142925.2571179-2-linus.walleij@linaro.org

drm/mcde: Fix RGB/BGR bug

I was confused when the graphics came out with blue
penguins on the DPI panel.

It turns out that the so-called "packed RGB666" mode
on the DSI formatter is incorrect: this mode is the
actual RGB888 mode, and the mode called RGB888 is
BGR888.

The claims that the MCDE had inverse RGB/BGR buffer
formats was wrong, so correct this and the buggy
register and everything is much more consistent, and
graphics look good on all targets, both DPI and
DSI.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Cc: phone-devel@vger.kernel.org
Cc: Stephan Gerhold <stephan@gerhold.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20201117175413.869871-1-linus.walleij@linaro.org

drm/mcde: Add new driver for ST-Ericsson MCDE

This adds a new DRM driver for the ST-Ericsson Multi Channel
Display Engine, MCDE display controller.

This hardware has three independent DSI hosts and can composit
and display several memory buffers onto an LCD display. It
was developed for several years inside of ST-Ericsson and
shipped with a few million mobile phones from Sony and Samsung,
as well as with the Snowball community development board.

The driver is currently pretty rudimentary but supports a
simple framebuffer so we can get penguins and graphics when
using these SoCs.

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190524092019.19355-1-linus.walleij@linaro.org