rpi-userland: new package

Introducing a package to build the userland part of the Raspberry,
needed by anyone who would want to build a rootfs for a RaspberryPi.

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
rpi-firmware: New package

Introducing a package to install pre-built binaries for the bootloader and the
GPU firmware for the RaspberryPi board.

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>