target/avr: CPU class: Add GDB support

This includes GDB hooks for reading from wnd wrtiting to AVR
registers, and xml register definition file as well.

[AM: Split a larger AVR introduction patch into logical units]
Suggested-by: Aleksandar Markovic <aleksandar.m.mail@gmail.com>
Co-developed-by: Michael Rolnik <mrolnik@gmail.com>
Co-developed-by: Sarah Harris <S.E.Harris@kent.ac.uk>
Signed-off-by: Michael Rolnik <mrolnik@gmail.com>
Signed-off-by: Sarah Harris <S.E.Harris@kent.ac.uk>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Aleksandar Markovic <aleksandar.m.mail@gmail.com>
Acked-by: Igor Mammedov <imammedo@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
[thuth: Fixed avr_cpu_gdb_read_register() parameter]
Signed-off-by: Thomas Huth <huth@tuxfamily.org>
Message-Id: <20200705140315.260514-7-huth@tuxfamily.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index dda872e..7833db3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -171,6 +171,7 @@
 M: Michael Rolnik <mrolnik@gmail.com>
 R: Sarah Harris <S.E.Harris@kent.ac.uk>
 S: Maintained
+F: gdb-xml/avr-cpu.xml
 F: target/avr/
 
 CRIS TCG CPUs