Accelerator fixes part 2: 8514/A.

Mix patterns are drawn at the correct position now instead of backwards.
Better handling of subsys/subcntl side.
As usual, better handling of the VGA on/off passthrough.
Better handling of the accelerator pitch (TODO: need a way to properly identify 640x480x256 in the pitch side).

src/include/86box/vid_8514a.h

@@ -83,6 +83,7 @@ typedef struct ibm8514_t {
     } accel;
 
     uint16_t test;
+    int ibm_mode;
 
     int v_total, dispend, v_syncstart, split,
         h_disp, h_disp_old, h_total, h_disp_time, rowoffset,
@@ -107,5 +108,6 @@ typedef struct ibm8514_t {
     int      blitter_busy;
     uint64_t blitter_time;
     uint64_t status_time;
+    int pitch;
 } ibm8514_t;
 #endif /*VIDEO_8514A_H*/