V4L/DVB (7910): usb: input layer dependency fixes

testing of the -tip tree found the following build failures on
2.6.26-rc3:

  drivers/built-in.o: In function `ttusb_dec_disconnect':
  ttusb_dec.c:(.text+0xa2c95): undefined reference to `input_unregister_device'

  drivers/built-in.o: In function `dvb_usb_read_remote_control':
  dvb-usb-remote.c:(.text+0xa6a94): undefined reference to `input_event'

with this config:

  http://redhat.com/~mingo/misc/config-Tue_May_20_03_48_57_CEST_2008.bad



these are due to the media/dvb/usb layer having dependencies on INPUT
functionality, without having that spelled out in the Kconfig file.

this patch makes that dependency explicit (for the drivers affected),
which solves the build error.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>