entry64: remove uart debug chatter
enable SMP in 64bit build

- in startothers() we pass entry32mp instead of entrymp as the
  address that entryother will jump to in 32bit mode
- don't initialize paging in entryother in the 64bit build
  since we defer that until we switch to 64bit mode
- entry32mp is an entrypoint midway through entry64.S that
  shares much of the startup code for the secondary core(s)
  with the bootstrap core
re-enable SMP in 64bit mode