All of them are switched by a single gate, which is part of the
IMX7D_LCDIF_PIXEL_ROOT_CLK clock. Hence using that clock also for
the AXI bus clock (clock-name "axi") makes sure the gate gets
enabled when accessing registers.
There seem to be no separate AXI display clock, and the clock is
optional. Hence remove the dummy clock.
This fixes kernel freezes when starting the X-Server (which
disables/re-enables the display controller).