This changes corrects the ioctl() operations for both the CX2388[578] analog
video and MPEG video device nodes to properly and consistently support
VIDIOC_G_CHIP_IDENT, VIDIOC_DBG_G_REGISTER and VIDIOC_DBG_S_REGISTER ioctl()s.

This caused some ioctl() support routines to be broken out into a separate
source file.

Now v4l2-dbg can be used to manipulate CX2388[578] and CX23417 registers
including the CX2388[57] functions handled by the cx25840 module.

This was done in anticipation of developing a new v4l2_subdev for the
integrated IR controller of the CX23888.
Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>