When doing

  echo 1 > /sys/devices/system/cpu/microcode/reload

in order to reload microcode, I get:

  microcode: Total microcode saved: 1
  BUG: using smp_processor_id() in preemptible [00000000] code: bash/2606
  caller is debug_smp_processor_id+0x17/0x20
  CPU: 1 PID: 2606 Comm: bash Not tainted 3.19.0-rc7+ #9
  Hardware name: LENOVO 2320CTO/2320CTO, BIOS G2ET86WW (2.06 ) 11/13/2012
   ffffffff81a4266d ffff8802131db808 ffffffff81666588 0000000000000007
   0000000000000001 ffff8802131db838 ffffffff812e6eef ffff8802131db868
   00000000000306a9 0000000000000010 0000000000000015 ffff8802131db848
  Call Trace:
   dump_stack
   check_preemption_disabled
   debug_smp_processor_id
   show_saved_mc
   ? save_microcode.constprop.8
   save_mc_for_early
   ? print_context_stack
   ? dump_trace
   ? __bfs
   ? mark_held_locks
   ? get_page_from_freelist
   ? trace_hardirqs_on_caller
   ? trace_hardirqs_on
   ? __alloc_pages_nodemask
   ? __get_vm_area_node
   ? map_vm_area
   ? __vmalloc_node_range
   ? generic_load_microcode
   generic_load_microcode
   ? microcode_fini_cpu
   request_microcode_fw
   reload_store
   dev_attr_store
   sysfs_kf_write
   kernfs_fop_write
   vfs_write
   ? sysret_check
   SyS_write
   system_call_fastpath
  microcode: CPU1: sig=0x306a9, pf=0x10, rev=0x15
  microcode: mc_saved[0]: sig=0x306a9, pf=0x12, rev=0x1b, toal size=0x3000, date = 2014-05-29

because we're using smp_processor_id() in preemtible context. And we
don't really need to use it there because the microcode container we're
dumping is global and CPU-specific info is irrelevant.

While at it, make pr_* stuff use "microcode: " prefix for easier
grepping and document how to enable the DEBUG build.
Signed-off-by: Borislav Petkov <bp@suse.de>