dt-bindings: usb: Clean-up "usb-phy" constraints

dt-bindings: usb: Clean-up "usb-phy" constraints

"usb-phy" has multiple type definitions. Unify the type with the looser
definition, phandle-array, as there are cases with multiple entries
(USB2 and USB3). However, the 'phandle-array' type alone is a bit
ambiguous. It can be either just an array of phandles or an array of
phandles plus args. "usb-phy" is the former and needs to constrain each
entry to a single phandle value.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20240124190725.1554080-1-robh@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>