V4L/DVB (7030): Kconfig: add missing selections for VIDEO_PVRUSB2

VIDEO_PVRUSB2 must select:
VIDEO_SAA711X, VIDEO_CX25840, VIDEO_MSP3400, and VIDEO_WM8775

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Acked-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>