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/nes.h

@@ -82,6 +82,26 @@
 #define COLOR_LIGHTBLUE         0x0E
 #define COLOR_GRAY3             0x0F
 
+/* Masks for joy_read */
+#define JOY_UP_MASK     0x10
+#define JOY_DOWN_MASK   0x20
+#define JOY_LEFT_MASK   0x40
+#define JOY_RIGHT_MASK  0x80
+#define JOY_BTN_1_MASK  0x01
+#define JOY_BTN_2_MASK  0x02
+#define JOY_BTN_3_MASK  0x04
+#define JOY_BTN_4_MASK  0x08
+
+#define JOY_BTN_A_MASK  JOY_BTN_1_MASK
+#define JOY_BTN_B_MASK  JOY_BTN_2_MASK
+#define JOY_SELECT_MASK JOY_BTN_3_MASK
+#define JOY_START_MASK  JOY_BTN_4_MASK
+
+#define JOY_BTN_A(v)    ((v) & JOY_BTN_A_MASK)
+#define JOY_BTN_B(v)    ((v) & JOY_BTN_B_MASK)
+#define JOY_SELECT(v)   ((v) & JOY_SELECT_MASK)
+#define JOY_START(v)    ((v) & JOY_START_MASK)
+
 /* Return codes of get_tv */
 #define TV_NTSC         0
 #define TV_PAL          1
@@ -90,17 +110,6 @@
 /* No support for dynamically loadable drivers */
 #define DYN_DRV         0
 
-/* Expanding upon joystick.h */
-#define JOY_BTN_A_IDX           4
-#define JOY_BTN_B_IDX           5
-#define JOY_SELECT_IDX          6
-#define JOY_START_IDX           7
-
-#define JOY_BTN_A(v)            ((v) & joy_masks[JOY_BTN_A_IDX])
-#define JOY_BTN_B(v)            ((v) & joy_masks[JOY_BTN_B_IDX])
-#define JOY_SELECT(v)           ((v) & joy_masks[JOY_SELECT_IDX])
-#define JOY_START(v)            ((v) & joy_masks[JOY_START_IDX])
-
 /* Define hardware */
 
 /* Picture Processing Unit */