arch:arm:boot:dts:overlays: Added waveshare 5.0inch, 6.25inch, and 8.8inch dsi screen description

Signed-off-by: eng33 <eng33@waveshare.com>

Author: eng33

arch/arm/boot/dts/overlays/README

@@ -5233,6 +5233,9 @@ Params: 2_8_inch                2.8" 480x640
         3_4_inch                3.4" 800x800 round
         4_0_inch                4.0" 480x800
         4_0_inchC               4.0" 720x720
+        5_0_inch                5.0" 720x1280
+        6_25_inch               6.25" 720x1560
+        8_8_inch                8.8" 480x1920
         7_0_inchC               7.0" C 1024x600
         7_9_inch                7.9" 400x1280
         8_0_inch                8.0" 1280x800