fpga: dfl: add dfl_fpga_check_port_id function.

This patch adds one common function in DFL framework. It uses
port_ops get_id callback to get port id and compare it with given
value. This function could be used as match function of the
dfl_fpga_cdev_find_port function.

Signed-off-by: Wu Hao <hao.wu@intel.com>
Acked-by: Alan Tull <atull@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>