arm64: zynqmp: add MAINTAINERS entry for Avnet UltraZed-EV

The board was added without adding a MAINTAINERS entry.

Fixes:

  $ ./tools/genboardscfg.py -f
  WARNING: no status info for 'avnet_ultrazedev_cc_v1_0_ultrazedev_som_v1_0'
  WARNING: no maintainers for 'avnet_ultrazedev_cc_v1_0_ultrazedev_som_v1_0'
  $

Reported-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>