drm/bridge/synopsys: dsi: driver-specific configuration of phy timings

The timing values for dw-dsi are often dependent on the used display and
according to Philippe Cornu will most likely also depend on the used phy
technology in the soc-specific implementation.

To solve this and allow specific implementations to define them as needed
add a new get_timing callback to phy_ops and call this from the dphy_timing
function to retrieve the necessary values for the specific mode.

Right now this handles the hs2lp + lp2hs where Rockchip SoCs need handling
according to the phy speed, while STM seems to be ok with static values.

changes in v5:
- rebase on 5.5-rc1
- merge into px30 dsi series to prevent ordering conflicts

changes in v4:
- rebase to make it directly fit on top of drm-misc-next after all

changes in v3:
- check existence of phy_ops->get_timing in __dw_mipi_dsi_probe()
- emit actual error when get_timing() call fails
- add tags from Philippe and Yannick

changes in v2:
- add driver-specific handling, don't force all bridge users to use
  the same timings, as suggested by Philippe

Suggested-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Reviewed-by: Philippe Cornu <philippe.cornu@st.com>
Tested-by: Yannick Fertre <yannick.fertre@st.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191209143130.4553-2-heiko@sntech.de