Added a few keyboard controller commands used by the AMI BIOS'es;

The port 92 handler in mem.c now flushes MMU cache when toggling the A20 gate;
Added ability to reload previous disc after ejecting it;
Fixed the START/STOP UNIT command for both SCSI and ATAPI;
Applied mainline PCem commit: All XT models can now use 64kb RAM. Patch from ecksemmess .

src/mem.c

@@ -2169,6 +2169,7 @@ void port_92_reset()
 	port_92_reg = 0;
 	mem_a20_alt = 0;
 	mem_a20_recalc();
+	flushmmucache();
 }
 
 uint32_t get_phys_virt,get_phys_phys;