Many fixes and improvements to the BIOS Extension ROM. (#33)

* Revert "Uploaded_2_9_2025"

This reverts commit ec79bbdbc9.

* Fixing DEBUG_IO builds.

* Make the IO port base a define.

* Fix CPU test to properly handle 808x vs V20.

* Improve timeout management logic.

* Improve SD Card initialization logic.

* Implement INT18h bootstrapping.

* Implementing a different test for processor type.

* Allow use with another fixed drive (eg: ESDI drive).

* Allow swapping driver ID between the BIOS disk and XTMax.

* Fix address of the ROM segment.

* Fixing missing STI at the top of the handler.

* Major rework of IO to use MOVSW.

* More code reorg and auto-detecting second drive.

* Update XTSD to use MOVSW.

* Add diagnostics program.

* Workaround for MS-DOS strange handling of interrupts.

* Use a lookup table for the memory map.

* Make the BootROM relocatable.

* Some more refactor of the Teensy code.

XTMax/Drivers/SDPP/HEADER.ASM

@@ -129,7 +129,7 @@ _header  DD -1    ; link to the next device
    DW DGROUP:STRATEGY   ; address of the strategy routine
    DW DGROUP:INTERRUPT;  "     "   "  interrupt   "
    DB 1     ; number of drives
-   DB 'SDCDv12'   ; DOS doesn't really use these bytes
+   DB 'SDCDv13'   ; DOS doesn't really use these bytes
 
 ;   The geometry (sectors/track, tracks/cylinder) defined in the BPB is rather
 ; arbitrary in the case of the TU58, but there are things to watch out for.