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 <[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
[rth: Squash Arduino adjustments from f4bug]
Tested-by: Richard Henderson <[email protected]>
Signed-off-by: Richard Henderson <[email protected]>
Signed-off-by: Aleksandar Markovic <[email protected]>
Acked-by: Thomas Huth <[email protected]>
Tested-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Thomas Huth <[email protected]>
Message-Id: <20200705140315[email protected]>