V4L/DVB (13100): cx23885: Add IR input keypress handling and enable for the HVR-1850

This changes adds IR Rx keypress input event handling to the CX23885 module.
This change specifically only adds input handling for IR devices implemented as
v4l2_subdevices, using only the pulse width mode (for now), and only with
RC-5 remotes.  The V4L-DVB infrastructure is missing too much to support RC-6
mode 6A as used in many media center remotes.   The grey Hauppauge RC-5 remote
and HVR-1850 IR receiver work now.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>