The code from [1] sets SYS_CTRL_1 to different values depending on the
desired clock phase (0, 1/4, 1/2 or 3/4). A clock phase of 0 aligns the
positive edge of the clock with the pixel data while other values delay
the clock by a fraction of the clock period. A clock phase of 1/2 aligns
the negative edge of the clock with the pixel data.

The driver currently hard codes SYS_CTRL_1 to 0x88 which corresponds to
aligning the positive edge of the clock with the pixel data. This won't
work correctly for panels that require aligning the negative edge of the
clock with the pixel data.

Adjust the clock phase to 0 if DRM_BUS_FLAG_PIXDATA_DRIVE_POSEDGE is
present in bus_flags, otherwise adjust the clock phase to 1/2 as
appropriate for DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE.

[1] https://github.com/tdjastrzebski/ICN6211-ConfiguratorSigned-off-by: Jonathan Liu <net147@gmail.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220523130144.444225-1-net147@gmail.com