Fix draw_string to support Grayscale
Fix draw_string to support Grayscale

iabdalkader/openmv,openmv/openmv,openmv/openmv,SmartArduino/openmv,SmartArduino/openmv,iabdalkader/openmv,kwagyeman/openmv,SmartArduino/openmv,iabdalkader/openmv,iabdalkader/openmv,openmv/openmv,openmv/openmv,kwagyeman/openmv,kwagyeman/openmv,kwagyeman/openmv,SmartArduino/openmv