[media] cx88: remove g_chip_ident

Remove g_chip_ident from cx88. Also remove the v4l2-chip-ident.h include.
The board code used defines from v4l2-chip-ident.h to tell the driver which
audio chip is used. Replace this with a cx88-specific enum.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>