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/atmos.h

@@ -113,6 +113,15 @@
 
 
 
+/* Masks for joy_read */
+#define JOY_UP_MASK     0x10
+#define JOY_DOWN_MASK   0x08
+#define JOY_LEFT_MASK   0x01
+#define JOY_RIGHT_MASK  0x02
+#define JOY_BTN_1_MASK  0x20
+
+
+
 /* No support for dynamically loadable drivers */
 #define DYN_DRV         0