monitor: added generation of documentation for hmp-commands-info.hx

monitor: added generation of documentation for hmp-commands-info.hx

It will be easier if you need to add info-commands to edit
only hmp-commands-info.hx, before this had to edit monitor.c and
hmp-commands.hx.

From the build point of view all documentation is saved into
qemu-monitor-info.texi which from now on is used for all user
documentation building.

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <1441899541-1856-5-git-send-email-den@openvz.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>