GameSettings: Set medium texture cache accuracy for Game Boy Player

Some games are showing frame flickering, e.g. Pokémon games when only
the text at the bottom of the screen is updating. GB/GBC games are
apparently especially affected, presumably due to the extra border.

Data/Sys/GameSettings/UGP.ini

@@ -6,3 +6,7 @@ HSPDevice = 2
 # Overclock to work around sporadic audio/video stream failures.
 Overclock = 1.25
 OverclockEnable = True
+
+[Video_Settings]
+# Fixes old frames being shown when a game updates the center/bottom of the screen without updating the top.
+SafeTextureCacheColorSamples = 512