tests/boot-serial: Test some Arduino boards (AVR based)

tests/boot-serial: Test some Arduino boards (AVR based)

Print out 'T' through serial port.

The Arduino Duemilanove is based on a AVR5 CPU, while the
Arduino MEGA2560 on a AVR6 CPU.

Signed-off-by: Michael Rolnik <mrolnik@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
[rth: Squash Arduino adjustments from f4bug]
Tested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Aleksandar Markovic <aleksandar.m.mail@gmail.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Thomas Huth <huth@tuxfamily.org>
Message-Id: <20200705140315.260514-29-huth@tuxfamily.org>