x86/IO-APIC: Drop function pointers from __ioapic_{read,write}_entry()

x86/IO-APIC: Drop function pointers from __ioapic_{read,write}_entry()

Function pointers are expensive, and the raw parameter is a constant at the
root of all call trees, meaning that it predicts very well with local branch
history.

Furthermore, the knock-on effects are quite impressive.

  $ ../scripts/bloat-o-meter xen-syms-before xen-syms-after
  add/remove: 0/4 grow/shrink: 3/9 up/down: 459/-823 (-364)
  Function                                     old     new   delta
  __ioapic_write_entry                          73     286    +213
  __ioapic_read_entry                           75     276    +201
  save_IO_APIC_setup                           182     227     +45
  eoi_IO_APIC_irq                              241     229     -12
  disable_IO_APIC                              296     280     -16
  mask_IO_APIC_setup                           272     240     -32
  __io_apic_write                               46       -     -46
  __io_apic_read                                46       -     -46
  io_apic_set_pci_routing                      985     930     -55
  __io_apic_eoi.part                           223     161     -62
  io_apic_write                                 69       -     -69
  io_apic_read                                  69       -     -69
  restore_IO_APIC_setup                        325     253     -72
  ioapic_guest_write                          1413    1333     -80
  clear_IO_APIC_pin                            447     343    -104
  setup_IO_APIC                               5148    4988    -160

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>