x86/alternatives: Add pr_fmt() to debug macros

... in order to have debug output prefixed with the pr_fmt text "SMP
alternatives:" which allows easy grepping:

  $ dmesg | grep "SMP alternatives"
  [    0.167783] SMP alternatives: alt table ffffffff8272c780, -> ffffffff8272fd6e
  [    0.168620] SMP alternatives: feat: 3*32+16, old: (x86_64_start_kernel+0x37/0x73 \
		  (ffffffff826093f7) len: 5), repl: (ffffffff8272fd6e, len: 5), pad: 0
  [    0.170103] SMP alternatives: ffffffff826093f7: old_insn: e8 54 a8 da fe
  [    0.171184] SMP alternatives: ffffffff8272fd6e: rpl_insn: e8 cd 3e c8 fe
  ...
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200615175315.17301-1-bp@alien8.de

arch/x86/kernel/alternative.c

@@ -53,7 +53,7 @@ __setup("noreplace-smp", setup_noreplace_smp);
 #define DPRINTK(fmt, args...)						\
 do {									\
 	if (debug_alternative)						\
-		printk(KERN_DEBUG "%s: " fmt "\n", __func__, ##args);	\
+		printk(KERN_DEBUG pr_fmt(fmt) "\n", ##args);		\
 } while (0)
 
 #define DUMP_BYTES(buf, len, fmt, args...)				\
@@ -64,7 +64,7 @@ do {									\
 		if (!(len))						\
 			break;						\
 									\
-		printk(KERN_DEBUG fmt, ##args);				\
+		printk(KERN_DEBUG pr_fmt(fmt), ##args);			\
 		for (j = 0; j < (len) - 1; j++)				\
 			printk(KERN_CONT "%02hhx ", buf[j]);		\
 		printk(KERN_CONT "%02hhx\n", buf[j]);			\