Removed joy_masks array.

So far the joy_masks array allowed several joystick drivers for a single target to each have different joy_read return values. However this meant that every call to joy_read implied an additional joy_masks lookup to post-process the return value.

Given that almost all targets only come with a single joystick driver this seems an inappropriate overhead. Therefore now the target header files contain constants matching the return value of the joy_read of the joystick driver(s) on that target.

If there indeed are several joystick drivers for a single target they must agree on a common return value for joy_read. In some cases this was alredy the case as there's a "natural" return value for joy_read. However a few joystick drivers need to be adjusted. This may cause some overhead inside the driver. But that is for sure smaller than the overhead introduced by the joy_masks lookup before.

!!! ToDo !!!

The following three joystick drivers become broken with this commit and need to be adjusted:
- atrmj8.s
- c64-numpad.s
- vic20-stdjoy.s

include/atari5200.h

@@ -87,6 +87,13 @@ extern void atr5200std_joy[];        /* referred to by joy_static_stddrv[] */
 #define COLOR_LIGHTBLUE         _gtia_mkcolor(HUE_BLUE,6)
 #define COLOR_GRAY3             _gtia_mkcolor(HUE_GREY,5)
 
+/* Masks for joy_read */
+#define JOY_UP_MASK     0x01
+#define JOY_DOWN_MASK   0x02
+#define JOY_LEFT_MASK   0x04
+#define JOY_RIGHT_MASK  0x08
+#define JOY_BTN_1_MASK  0x10
+
 /* get_tv return values */
 #define AT_NTSC     0
 #define AT_PAL      1
@@ -104,4 +111,4 @@ extern void atr5200std_joy[];        /* referred to by joy_static_stddrv[] */
 #define ANTIC (*(struct __antic*)0xD400)
 
 /* End of atari5200.h */
-#endif /* #ifndef _ATARI5200_H */
+#endif