Introduced the notion of a standard serial driver.

There's no target with more than one serial driver (and I don't see that change anytime soon) so it's a no-brainer to apply the standard driver concept to serial drivers.

libsrc/atari/ser_stat_stddrv.s

@@ -0,0 +1,22 @@
+;
+; Address of the static standard serial driver
+;
+; Oliver Schmidt, 2022-12-22
+;
+; const void ser_static_stddrv[];
+;
+
+        .export _ser_static_stddrv
+        .ifdef  __ATARIXL__
+        .import _atrxrdev_ser
+        .else
+        .import _atrrdev_ser
+        .endif
+
+.rodata
+
+        .ifdef  __ATARIXL__
+_ser_static_stddrv := _atrxrdev_ser
+        .else
+_ser_static_stddrv := _atrrdev_ser
+        .endif

libsrc/atari/ser_stddrv.s

@@ -0,0 +1,18 @@
+;
+; Name of the standard serial driver
+;
+; Oliver Schmidt, 2022-12-22
+;
+; const char ser_stddrv[];
+;
+
+        .export _ser_stddrv
+
+.rodata
+
+_ser_stddrv:
+        .ifdef  __ATARIXL__
+                .asciiz "atrxrdev.ser"
+        .else
+                .asciiz "atrrdev.ser"
+        .endif