zynq: use pl310 device tree bindings

The Zynq has a PL310 L2 cache controller.  Convert in-tree uses to using
the device tree.

Signed-off-by: Josh Cartwright <josh.cartwright@ni.com>
Cc: John Linn <john.linn@xilinx.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Michal Simek <michal.simek@xilinx.com>