MAINTAINERS: Add Hao and Yilun as maintainers

Hao and Yilun have agreed to help out with maintenance.
Both have been active in the Linux FPGA community for a long time
and we need backups for vacation and load-balancing.

Cc: Xu Yilun <yilun.xu@intel.com>
Cc: Wu Hao <hao.wu@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Acked-by: Wu Hao <hao.wu@intel.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>