dt-bindings: usb: mtk-xhci: Make all clocks required

All of the clocks listed in the binding are always wired to the XHCI
controller hardware blocks on all SoCs. The reason some clocks were made
optional in the binding was to account for the fact that depending on
the SoC, some of the clocks might be fixed (ie not controlled by
software).

Given that the devicetree should represent the hardware, make all clocks
required in the binding. Subsequent patches will make the DTS changes to
specify fixed-clocks for the clocks that aren't controllable.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Link: https://lore.kernel.org/r/20220623193702.817996-3-nfraprado@collabora.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>