eudev: Add group sgx to eudev package

Fix startup warning:

  udevd[171]: specified group 'sgx' unknown

This mirrors the change in bab455cd ("systemd: add group sgx to udev
package") for systemd-udev.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>