Rename regression test 2020 to reflect the CPU configuration

Cycle counting is CPU-specific.  The 2020 test exercises the
65816, but there are things unique to 6502 and 65C02 that should
also be checked if we want to be thorough.

No changes to the test itself.

Asm65/OpDef.cs

@@ -2049,6 +2049,7 @@ namespace Asm65 {
             Opcode = 0x6c,
             AddrMode = AddressMode.AbsInd,
             CycDef = 5 | (int)(CycleMod.OneIf65C02)
+            // takes one extra cycle on CMOS 6502 if low byte is 0xff?? (it also has a bug)
         };
         public static readonly OpDef OpADC_Abs = new OpDef(OpADC) {
             Opcode = 0x6d,

SourceGen/SGTestData/Expected/2020-cycle-counts-65816_cc65.cfg

@@ -1,4 +1,4 @@
-# 6502bench SourceGen generated linker script for 2020-cycle-counts
+# 6502bench SourceGen generated linker script for 2020-cycle-counts-65816
 MEMORY {
     MAIN: file=%O, start=%S, size=65536;
 #    MEM000: file=%O, start=$10f0, size=126;