drm: Add standardized boolean props

Not a new type exposed to userspace, just a standard way to create
them since between range, bitmask and enum there's 3 different ways to
pull out a boolean prop.

Also add the kerneldoc for the recently added new prop types, which
Rob forgot all about.

v2: Fixup kerneldoc, spotted by Rob.

Cc: Rob Clark <robdclark@gmail.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>