Add emulation of IBM PS/1 Model 2121.

As part of this :
- FDC Specify command now completes immediately
- Implemented keyboard system flag status
- Added ability to remap 384kb reserved memory to above extended memory

src/ibm.h

@@ -333,7 +333,8 @@ enum
         ROM_REVENGE,
         ROM_IBMPS1_2011,
         ROM_DESKPRO_386,
-	
+        ROM_IBMPS1_2121,
+        	
         ROM_MAX
 };