Various 486 improvements

- Added SL-Enhanced versions of Intel 486 CPUs and Enhanced AMD Am486DX2/DX4 CPUs
- Cleaned up the 486 CPU types and updated intel_4x0.c to reflect this
- Fixed some incorrect EDX reset and CPUID values
- Blacklisted non-SMM capable 486 CPUs on the Soyo 4SA2 motherboard
- Merged the non-OverDrive and OverDrive Intel DX4s because of further research confirming them to be functionally identical
- Removed SMM support on early 486 CPUs

src/device/keyboard_at.c

@@ -1061,7 +1061,7 @@ write_output(atkbd_t *dev, uint8_t val)
 		/* Pin 0 selected. */
 		softresetx86(); /*Pulse reset!*/
 		cpu_set_edx();
-		smbase = is_486_org ? 0x00060000 : 0x00030000;
+		smbase = 0x00030000;
 	}
     }
     /* Mask off the A20 stuff because we use mem_a20_key directly for that. */