uio: dfl: add IOPLL user-clock feature id

Add a Device Feature List (DFL) feature id [1] for the configurable
IOPLL user clock source, which can be used to configure the clock
speeds that are used for RTL logic that is programmed into the
Partial Reconfiguration (PR) region of an FPGA.

The IOPLL user-space driver [2] contains frequency tables [3]
with the specific user clock frequencies for an implementation.

For each desired frequency, the table values are produced by calling
the quartus tool, the same tool that generates the IOPLL RTL logic.
The quartus tool allows the RTL designer to select different options
which can affect the table values. The table-driven, user-space
driver allows for supporting future, modified implementations and
provides users the ability to modify the IOPLL implementation.

[1] https://github.com/OPAE/dfl-feature-id
[2] https://github.com/OPAE/opae-sdk/blob/a494f54a9f0356d0425edbff228f0254a4c70303/libraries/plugins/xfpga/usrclk/fpga_user_clk.c
[3] https://github.com/OPAE/opae-sdk/blob/a494f54a9f0356d0425edbff228f0254a4c70303/libraries/plugins/xfpga/usrclk/fpga_user_clk_freq.h

Acked-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Russ Weight <russell.h.weight@intel.com>
Signed-off-by: Peter Colberg <peter.colberg@intel.com>
Link: https://lore.kernel.org/r/20220831204851.4683-1-peter.colberg@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>