kernel: Add kmod-sfc-siena for Solarflare SFN5000/6000 series NICs

kernel: Add kmod-sfc-siena for Solarflare SFN5000/6000 series NICs

kmod-sfc should add support for Solarflare SFC9000 series based cards.
However after kernel 5.19, support for the 'Siena' subclass of
SFN5000/6000 devices has been separated out since they went EOL as they
are no longer being actively developed. As kmod-sfc no longer provides
driver support for these cards and hasn't since kernel 5.2, a new kernel
module is needed to support these 10Gb Ethernet cards. More info here:
https://cateee.net/lkddb/web-lkddb/SFC_SIENA.html and here:
https://www.phoronix.com/news/Solarflare-SFC-Siena-Linux-5.19

The module can be compiled in separately and works if kernel is custom
compiled;

OpenWRT has made these changes already with the SFC 'falcon' subclass of
drivers already. See 3c5d70a and e5ba6e9

This is building on excellent work by @ynezz and @nasbdh9

Signed-off-by: Steve Wavler <trenchcoatjedi@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/19647
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>