This adds the CPU or thread number to printk messages. This helps a
lot when deciphering concurrent oopses that have been interleaved.

Example output, of PID1 (T1) triggering a warning:

  [    1.581678][    T1] WARNING: CPU: 0 PID: 1 at crypto/rsa-pkcs1pad.c:539 pkcs1pad_verify+0x38/0x140
  [    1.581681][    T1] Modules linked in:
  [    1.581693][    T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.5.0-rc5-gcc-8.2.0-00121-gf84c2e595927-dirty #1515
  [    1.581700][    T1] NIP:  c000000000207d64 LR: c000000000207d3c CTR: c000000000207d2c
  [    1.581708][    T1] REGS: c0000000fd2e7560 TRAP: 0700   Not tainted  (5.5.0-rc5-gcc-8.2.0-00121-gf84c2e595927-dirty)
  [    1.581712][    T1] MSR:  9000000000029033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR: 44000222  XER: 00040000
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200520121257.961112-1-mpe@ellerman.id.au