feat: Add dvb-usb-dvbsky extension for MyGica T230C DVB-T/T2/C USB stick

[rokoucha]

This PR adds the dvb-usb-dvbsky extension for DVBSky USB DVB devices, including the MyGica T230C DVB-T/T2/C USB stick.

The required kernel modules were enabled in siderolabs/pkgs#1572.
This extension packages the DVB USB modules and firmware needed by these devices, following the existing dvb-cx23885 extension pattern.

The module can be enabled with the following Talos machine config:

machine:
  kernel:
    modules:
      - name: dvb_usb_dvbsky

Built successfully with PKGS=v1.14.0-alpha.0-71-gaa9fe00

Note: The module set was checked on an Arch Linux host with a physical MyGica T230C device, which was recognised successfully.

si2157                 32768  2
si2168                 28672  2
dvb_usb_dvbsky         32768  2
dvb_usb_v2             53248  1 dvb_usb_dvbsky
m88ds3103              45056  1 dvb_usb_dvbsky
dvb_core              217088  4 dvb_usb_v2,dvb_usb_dvbsky
videobuf2_vmalloc      20480  1 dvb_core
videobuf2_common       94208  3 videobuf2_vmalloc,dvb_core,videobuf2_memops
i2c_mux                16384  2 m88ds3103,si2168
mc                     90112  4 si2157,dvb_usb_v2,dvb_core,videobuf2_common