usb: Add explicit of.h of_platform.h include

Several USB drivers use of_platform_* functions which are declared in
of_platform.h. of_platform.h gets implicitly included by of_device.h,
but that is going to be removed soon. Nothing else depends on of_device.h
so it can be dropped.

Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Acked-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230410232639.1561152-1-robh@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>