Trantor SCSI changes of the day (April 2nd, 2025)

1. The PAS SCSI controller driver mamv1.sys dislikes having bits 0-6 set when a transfer has completed, take account from this, fixes mamv1.sys incomplete CD transfers (bits 0-6 get re-enabled when the transfer is ongoing).
2. I now understand why the T128 doesn't have a block count register, it does the block count manually from the SCSI layer directly, this fixes Pseudo-DMA transfers when using, e.g.: CD transfers using a sector size of 2340 bytes.

src/include/86box/scsi_device.h

@@ -467,9 +467,10 @@ typedef struct scsi_bus_t {
     int                msgout_pos;
     int                is_msgout;
     int                state;
-    int                dma_on_pio_enabled;
 
     uint32_t           bus_phase;
+    uint32_t           total_len;
+    uint32_t           data_repeat;
 
     double             period;
     double             speed;