tests/boot_linux_console: Add a test for the Raspberry Pi 2

tests/boot_linux_console: Add a test for the Raspberry Pi 2

Similar to the x86_64/pc test, it boots a Linux kernel on a raspi2
board and verify the serial is working.

The kernel image and DeviceTree blob are built by the Raspbian
project (based on Debian):
https://www.raspbian.org/RaspbianImages
as recommended by the Raspberry Pi project:
https://www.raspberrypi.org/downloads/raspbian/

If ARM is a target being built, "make check-acceptance" will
automatically include this test by the use of the "arch:arm" tags.

Alternatively, this test can be run using:

    $ avocado run -t arch:arm tests/acceptance
    $ avocado run -t machine:raspi2 tests/acceptance

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Tested-by: Cleber Rosa <crosa@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20191028073441.6448-21-philmd@redhat.com>
Signed-off-by: Cleber Rosa <crosa@redhat.com>