[media] mx2_camera: Remove i.mx25 support

i.MX25 support has been broken for several releases
now and nobody seems to care about it.

Signed-off-by: Javier Martin <javier.martin@vista-silicon.com>
[g.liakhovetski@gmx.de: rebased on top of cpu_is_mx27() removal]
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>