Add the clock dt-binding file for i.MX8ULP.

For pcc node, it will also be used as a reset controller,
so add the '#reset-cells' property description and add the
pcc reset IDs.
Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Link: https://lore.kernel.org/r/20210914065208.3582128-2-ping.bai@nxp.comSigned-off-by: Abel Vesa <abel.vesa@nxp.com>