delta: Add print_radius option to customize valid XY radius

Add ability to override the default XY move checking radius.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

config/example-delta.cfg

@@ -107,6 +107,13 @@ delta_radius: 174.75
 #   axis towers. This parameter may also be calculated as:
 #    delta_radius = smooth_rod_offset - effector_offset - carriage_offset
 #   This parameter must be provided.
+#print_radius:
+#   The radius (in mm) of valid toolhead XY coordinates. One may use
+#   this setting to customize the range checking of toolhead moves. If
+#   a large value is specified here then it may be possible to command
+#   the toolhead into a collision with a tower. The default is to use
+#   delta_radius for print_radius (which would normally prevent a
+#   tower collision).
 
 # The delta_calibrate section enables a DELTA_CALIBRATE extended
 # g-code command that can calibrate the tower endstop positions and