ARM: at91: pm: Tie the USB clock mask to the pmc

The USB clocks mask (uhp_udp_mask) depends on the pmc. Tie it to the pmc id
instead of the SoC.

Acked-by: Wenyou Yang <wenyou.yang@atmel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>