Cleanup/bugfix HPET driver:

    - hpet_init() could return failure with driver still registered with ACPI
    - driver add() functions were marked __init, but can be called any time
      until driver is unregistered (not a real problem until HPETs can be
      hotplugged)
    - time interpolator registration now done in driver add() path, so we can
      support removal of HPETs someday
    - physical MMIO address should be printed, not ioremapped address
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>