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/cpu/x86.c

@@ -281,7 +281,7 @@ reset_common(int hard)
     smi_block = 0;
 
     if (hard) {
-	smbase = is_486_org ? 0x00060000 : 0x00030000;
+	smbase = 0x00030000;
 	ppi_reset();
     }
     in_sys = 0;