This commit:
1. Renames beeline-trx recipe in mt7621.mk to arcadyan-trx. The recipe
is necessary for:
- MTS WG430223 (Arcadyan WG430223)
- Beeline Smartbox Flash (Arcadyan WG443223)
2. Allows specify custom trx magic which is different for the routers
mentined above.
Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>