V4L/DVB (7116): budget-av: Add support for KNC TV Station Plus X4

Add support for KNC TV Station Plus X4, sub-system id 0x1894:0x0015.
Based on a patch submitted by Johannes Deisenhofer.

Thanks-to: Johannes Deisenhofer <jo.deisenhofer@googlemail.com>
Signed-off-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>