usb: gadget: mv_u3d: drop ARCH dependency

this driver compiles fine everywhere which
means we can use linux-next to compile it
for us frequently.

By dropping the arch dependency, we also
ensure driver writers don't add virtual
arch-depdencies to the driver by e.g. using
the wrong headers.

While at that, fix Marvell's USB3 PHY dependency,
that's the driver which depends on CPU_MM3, not
mv_u3d_core.

Signed-off-by: Felipe Balbi <balbi@ti.com>