The Zynq uses the cortex-a9-gic.  This eliminates the need to hardcode
register addresses.
Signed-off-by: NJosh Cartwright <josh.cartwright@ni.com>
Cc: John Linn <john.linn@xilinx.com>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Tested-by: NMichal Simek <michal.simek@xilinx.com>