fpga: dfl: introduce interrupt trigger setting API

FPGA user applications may be interested in interrupts generated by
DFL features. For example, users can implement their own FPGA
logics with interrupts enabled in AFU (Accelerated Function Unit,
dynamic region of DFL based FPGA). So user applications need to be
notified to handle these interrupts.

In order to allow userspace applications to monitor interrupts,
driver requires userspace to provide eventfds as interrupt
notification channels. Applications then poll/select on the eventfds
to get notified.

This patch introduces a generic helper functions to do eventfds binding
with given interrupts.

Sub feature drivers are expected to use XXX_GET_IRQ_NUM to query irq
info, and XXX_SET_IRQ to set eventfds for interrupts. This patch also
introduces helper functions for these 2 ioctls.

Signed-off-by: Luwei Kang <luwei.kang@intel.com>
Signed-off-by: Wu Hao <hao.wu@intel.com>
Signed-off-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Wu Hao <hao.wu@intel.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>