Registering the dsi host with its ops before getting dsi->regs iswil => will
simply wrong: even though there's nothing (for now) asynchronously
calling those ops before the end of the probe function, installing
ops that are using iospace(s) and clocks before even initializing
those is too fragile.
Register the DSI host after getting clocks, iospace and PHY.
This wil also allow to simplify the error paths in a later commit.