lib: add pr_debug() macro

Add the pr_debug() macro so that:

  #ifdef DEBUG
  	printf("foo");
  #endif

can be replaced by:

  	pr_debug("foo");

Apply the pr_debug() macro wherever relevant.

Currently, there is no consensus whether debug messages should be
printed on stdout or stderr. Most of the modules: canbusload.c,
candump.c and canlogserver.c use stdout but
mcp251xfd/mcp251xfd-dev-coredump.c uses stderr. Harmonize the behavior
by following the major trend and make
mcp251xfd/mcp251xfd-dev-coredump.c also output to stdout.

slcanpty.c does a #define DEBUG, meaning that debug is always turned
on for this file. Remove this and make debug an option like every
other files.

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20221114163848.3398-5-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

mcp251xfd/mcp251xfd-dev-coredump.c

@@ -17,18 +17,10 @@
 
 #include <linux/kernel.h>
 
+#include "lib.h"
 #include "mcp251xfd.h"
 #include "mcp251xfd-dump-userspace.h"
 
-#define pr_err(fmt, args...)    fprintf(stderr, fmt, ##args)
-#define pr_no(fmt, args...)     while (0) { fprintf(stdout, fmt, ##args); }
-
-#ifdef DEBUG
-#define pr_debug(fmt, args...) pr_err(fmt, ##args)
-#else
-#define pr_debug(fmt, args...) pr_no(fmt, ##args)
-#endif
-
 
 struct mcp251xfd_dump_iter {
 	const void *start;