Split adb.c into adb.c, adb-mouse.c and adb-kbd.c

It makes the code clearer to separate the bus implementation
from the devices one.

Replace ADB_DPRINTF() with trace events (and adding new ones in adb-kbd.c).
Some minor changes to make checkpatch.pl happy.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20171220121406.24056-1-laurent@vivier.eu>
