Add AVR related definitions into QEMU, make AVR support buildable.

[AM: Remove word 'Atmel' from filenames and all elements of code]
Suggested-by: Aleksandar Markovic <aleksandar.m.mail@gmail.com>
Signed-off-by: Michael Rolnik <mrolnik@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Aleksandar Markovic <aleksandar.m.mail@gmail.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Signed-off-by: Thomas Huth <huth@tuxfamily.org>
Message-Id: <20200705140315.260514-23-huth@tuxfamily.org>
[PMD: Fixed @avr tag in qapi/machine.json]
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>