compositor-rdp: Add an option to disable client initiated resizes

compositor-rdp: Add an option to disable client initiated resizes

This patch adds an option to the RDP compositor to disable
desktop resizes initiated by RDP peer. The current behaviour
is that if an incoming RDP peer suggests a resolution that is
not the current one, a mode_switch() is done and the desktop is
resized to that new resolution. This new flag allows to disable
that behaviour. If the flag is set, the new behaviour is that the
RDP peer will be instructed to resize to the size of the desktop.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>