package/edk2-platforms: new package

EDK2 firmware is usually built from two sources; the core EDK2
environment, and additional platform description files maintained
separately. This package adds the latter set of description files to
staging so that the core EDK2 package can build with these for certain
platforms during the building process.

Signed-off-by: Dick Olsson <hi@senzilla.io>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>