DRAFT: drm: rp1: rp1-vec: Add a parameter to set DRM picture aspect ratio

[njhollinghurst]

Experimentally, allow setting picture_aspect_ratio field in all advertised DRM modes. This has no other effect on VEC's behaviour (and perhaps has no useful effects at all...)

It is set via a module parameter drm-rp1-vec.par which can be set from the command line, or later using sysfs. A value of 1 means 4:3, 2 means 16:9.