Use the local APIC timer to drive the various kernel clocks on SMP machines

rather than forwarding interrupts from the clock devices around using IPIs:
- Add an IDT vector that pushes a clock frame and calls
  lapic_handle_timer().
- Add functions to program the local APIC timer including setting the
  divisor, and setting up the timer to either down a periodic countdown
  or one-shot countdown.
- Add a lapic_setup_clock() function that the BSP calls from
  cpu_init_clocks() to setup the local APIC timer if it is going to be
  used.  The setup uses a one-shot countdown to calibrate the timer.  We
  then program the timer on each CPU to fire at a frequency of hz * 3.
  stathz is defined as freq / 23 (hz * 3 / 23), and profhz is defined as
  freq / 2 (hz * 3 / 2).  This gives the clocks relatively prime divisors
  while keeping a low LCM for the frequency of the clock interrupts.
  Thanks to Peter Jeremy for suggesting this approach.
- Remove the hardclock and statclock forwarding code including the two
  associated IPIs.  The bitmap IPI handler has now effectively degenerated
  to just IPI_AST.
- When the local APIC timer is used we don't turn the RTC on at all, but
  we still enable interrupts on the ISA timer 0 (i8254) for timecounting
  purposes.

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