Report ready DVD status to CDVDMAN

* Early on the IOP continiously reads from 0x1F402005 which
is the N command status register [1], to know if it's
ready or not. So it be safe, let's report that the drive is ready
by returning 0x40 (bit 6 set)

[1] https://psi-rockin.github.io/ps2tek/#cdvdioports

src/cpu/iop/iop.h

@@ -173,6 +173,8 @@ namespace iop
         {
         case 0 ... 0x1fffff:
             return *(T*)&ram[paddr];
+        case 0x1f402005:
+            return 0x40; /* Report to CDVDMAN, the DVD drive is ready */
         case 0x1f801100 ... 0x1f80112c:
         case 0x1f801480 ... 0x1f8014ac:
             return timers.read(paddr);