This change adds a skeletal implementation of a v4l2_subdevice to provide
encapsulation and abstraction of the CX23888's integrated consumer infrared
controller.  This change also instantiates the cx23888_ir subdev for the
HVR-1850 which has IR hardware physically wired up to a CX23888.

The cx23888_ir subdev code is being written with long-term objectives to:
1. port it to the cx25840 module for the CX2584x, CX2583x, CX23885, & CX231xx
   IR controllers
2. possibly port it to the cx18 module for the CX23418 IR controller
3. have the IR subdevice accessed abstractly in the cx23885 module, so the
   driver can ignore the difference between the CX23885 and CX23888.
Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>