xenfb: Use Input Handlers directly

xenfb: Use Input Handlers directly

Avoid the unneccessary calls through the input-legacy.c file by
using the qemu_input_handler_*() calls directly. This did require
reworking the event and sync handlers to use the reverse mapping
from qcode to linux using qemu_input_qcode_to_linux().
Removes the scancode2linux mapping, and supporting documention.

Signed-off-by: Owen Smith <owen.smith@citrix.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>