powerpc/ppc64: Print CPU/MMU/FW features at boot

"Helps debug funky firmware issues".

After:
  Starting Linux PPC64 #108 SMP Wed Aug 6 19:04:51 EST 2014
  -----------------------------------------------------
  ppc64_pft_size    = 0x1a
  phys_mem_size     = 0x200000000
  cpu_features      = 0x17fc7a6c18500249
    possible        = 0x1fffffff18700649
    always          = 0x0000000000000040
  cpu_user_features = 0xdc0065c2 0xee000000
  mmu_features      = 0x5a000001
  firmware_features = 0x00000001405a440b
  htab_hash_mask    = 0x7ffff
  -----------------------------------------------------

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>