drm: tiny: st7735r: Prepare for adding support for more displays

Currently the st7735r driver supports only a single display panel.
Prepare for adding support for other display panels by factoring out the
display-specific parameters in struct st7735r_cfg.

For now, the following parameters can be configured:
  - Display resolution,
  - Horizontal/vertical display offsets,
  - Read-write versus read-only controllers,
  - RGB versus BGR color component ordering.

Rename jd_t18003_t01_pipe_enable() and jd_t18003_t01_pipe_funcs() to
st7735r_pipe_enable() resp. st7735r_pipe_funcs(), as they are not really
specific to the Jianda JD-T18003-T01 display anymore.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200115124548.3951-5-geert+renesas@glider.be