x86: mpparse: clean up code by introducing a few helper functions

Impact: cleanup

Refactor the MP-table parsing code via the introduction of the
following helper functions:

  skip_entry()
  smp_reserve_bootmem()
  check_irq_src()
  check_slot()

To simplify the code flow and to reduce the size of the
following oversized functions: smp_read_mpc(), smp_scan_config().

There should be no impact to functionality.

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>