boards: shields: rk055hdmipi4ma0: raise MIPI DSI bit clock for RT1170

The RT1170 MIPI DPHY requires a faster clock frequency setting for
the MIPI DPHY, or the pixel packet counts for the HFP, HBP, and HSA will
be incorrect, and the DSI transfers will stall. Raise the target DPHY
clock frequency to resolve this.

Fixes #78299

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>