powerpc/powernv/mce: Reduce MCE console logs to lesser lines.

Also add cpu number while displaying MCE log. This will help cleaner
logs when MCE hits on multiple cpus simultaneously.

Before the changes the MCE output was:

  Severe Machine check interrupt [Recovered]
    NIP [d00000000ba80280]: insert_slb_entry.constprop.0+0x278/0x2c0 [mcetest_slb]
    Initiator: CPU
    Error type: SLB [Multihit]
      Effective address: d00000000ba80280

After this patch series changes the MCE output will be:

  MCE: CPU80: machine check (Warning) Host SLB Multihit [Recovered]
  MCE: CPU80: NIP: [d00000000b550280] insert_slb_entry.constprop.0+0x278/0x2c0 [mcetest_slb]
  MCE: CPU80: Probable software error (some chance of hardware cause)

UE in host application:

  MCE: CPU48: machine check (Severe) Host UE Load/Store DAR: 00007fffc6079a80 paddr: 0000000f8e260000 [Not recovered]
  MCE: CPU48: PID: 4584 Comm: find NIP: [0000000010023368]
  MCE: CPU48: Hardware error

and for MCE in Guest:

  MCE: CPU80: machine check (Warning) Guest SLB Multihit DAR: 000001001b6e0320 [Recovered]
  MCE: CPU80: PID: 24765 Comm: qemu-system-ppc Guest NIP: [00007fffa309dc60]
  MCE: CPU80: Probable software error (some chance of hardware cause)

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>