drm/mcde: dsi: Fix duplicated DSI connector

Using a (single) DSI display with MCDE currently results in
two "connected" connectors:

  Connector: DSI-1
          id             : 34
          encoder id     : 0
          conn           : connected
          size           : 0x0 (mm)
          count_modes    : 0
          count_props    : 5
          props          : 1 2 5 6 4
          count_encoders : 1
          encoders       : 33
  Connector: DSI-2
          id             : 35
          encoder id     : 33
          conn           : connected
          size           : 53x89 (mm)
          count_modes    : 1
          count_props    : 5
          props          : 1 2 5 6 4
          count_encoders : 1
          encoders       : 33
    Mode: "480x800" 480x800 60

Although both show up as connected, the first one does not have
any size and no available modes. This confuses userspace tools
(e.g. kmscube) who look for available modes for the first connector.

The reason for the duplicated connector is that mcde_dsi.c and the
DRM panel bridge helper both set up a DSI connector, with more or less
the same code. The connector set up by the DRM panel bridge is the
one that is correctly set up in the example above.

Therefore we can just remove the connector setup from mcde_dsi.c
and let the DRM core handle all the hard work.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191106165835.2863-6-stephan@gerhold.net