Modernize and flavourize RT Extension ports

Convert the RT{40,42,44} options to new rt42 and rt44 flavours.

Drop all references to www/rt40 -- no longer in ports

Default flavour is rt44, but several of these modules only support
rt42.

Ensure @rt42 flavour conflicts with www/rt44 port and vice-versa

Re-order various sections and re-roll one patch to placate portlint

Reviewed by: portmgr (mat)
Differential Revision: https://reviews.freebsd.org/D17285