x86/alternatives: Add pr_fmt() to debug macros

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