rdp: Calculate frame times from mode refresh rate

Instead of hard coding a 16ms refresh interval, use the refresh rate
from the current mode to determine when the next frame should be.

Currently, we still hard code the refresh rate, so this will end up
with roughly the same value we've been using, but in the future
we'll allow setting it via command line.

Co-authored-by: Steve Pronovost <spronovo@microsoft.com>
Co-authored-by: Brenton DeGeer <brdegeer@microsoft.com>
Signed-off-by: Hideyuki Nagase <hideyukn@microsoft.com>
Signed-off-by: Steve Pronovost <spronovo@microsoft.com>
Signed-off-by: Brenton DeGeer <brdegeer@microsoft.com>