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

libsrc/apple2/joy/a2.stdjoy.s

@@ -46,17 +46,6 @@ PREAD   :=      $FB1E   ; Read paddle in X, return AD conv. value in Y
 
         .addr   $0000
 
-; Button state masks (8 values)
-
-        .byte   $10
-        .byte   $20
-        .byte   $04
-        .byte   $08
-        .byte   $40
-        .byte   $80
-        .byte   $00             ; Future expansion
-        .byte   $00             ; Future expansion
-
 ; Jump table
 
         .addr   INSTALL
@@ -119,7 +108,7 @@ READJOY:
         lda     BUTN0-1,x       ; Check button (1, 3)
         asl
         tya
-        ror                     ; FIRE DOWN !UP RIGHT !LEFT 0 0 0
+        ror                     ; BTN DOWN !UP RIGHT !LEFT 0 0 0
 
         ; Read secondary button
         tay
@@ -130,10 +119,10 @@ READJOY:
         lda     BUTN0-1,x       ; Check button (2, 0)
         asl
         tya
-        ror                     ; FIRE2 FIRE DOWN !UP RIGHT !LEFT 0 0
+        ror                     ; BTN2 BTN DOWN !UP RIGHT !LEFT 0 0
 
         ; Finalize
-        eor     #%00010100      ; FIRE2 FIRE DOWN UP RIGHT LEFT 0 0
+        eor     #%00010100      ; BTN2 BTN DOWN UP RIGHT LEFT 0 0
         ldx     #$00
         bit     $C080           ; Switch in LC bank 2 for R/O
         rts