Replaced builtin linker configs with ordinary .cfg files.

The benefits are:
- Independency of ld65 build from perl
- More transparent behaviour

cfg/c64-asm.cfg

@@ -0,0 +1,18 @@
+FEATURES {
+    STARTADDRESS: default = $0801;
+}
+SYMBOLS {
+    __LOADADDR__: type = import;
+}
+MEMORY {
+    LOADADDR: file = %O, start = %S - 2, size = $0002;
+    RAM:      file = %O, start = %S,     size = $D000 - %S;
+}
+SEGMENTS {
+    LOADADDR: load = LOADADDR, type = ro;
+    EXEHDR:   load = RAM,      type = ro,  optional = yes;
+    CODE:     load = RAM,      type = rw,  optional = yes;
+    RODATA:   load = RAM,      type = ro,  optional = yes;
+    DATA:     load = RAM,      type = rw,  optional = yes;
+    BSS:      load = RAM,      type = bss, optional = yes;
+}