Use mainboard_interrupt_handlers everywhere

Use mainboard_interrupt_handlers everywhere

The previous commit provides a mainboard_interrupt_handlers
implementation YABEL with identical semantics to the
x86emu one, so let's use it in both cases.

This eliminates the need for the int15_install()
indirection, so let's drop that, too.

Generated using the following coccinelle patch and
manual cleanups (empty #if/#endif):
  @@
  type T;
  identifier FUNCARR;
  expression INT, HANDLER;
  @@
  -typedef T yabel_handleIntFunc;
  -extern yabel_handleIntFunc FUNCARR[256];
  -FUNCARR[INT] = HANDLER;
  +mainboard_interrupt_handlers(INT, &HANDLER);

  @@
  @@
  -void int15_install(void)
  -{
  -mainboard_interrupt_handlers(0x15, &int15_handler);
  -}

  @@
  @@
  -void int15_install(void)
  -{
  -mainboard_interrupt_handlers(0x15, &int15_handler); ... mainboard_interrupt_handlers(0x15, &int15_handler);
  -}

  @@
  @@
  -int15_install();
  +mainboard_interrupt_handlers(0x15, &int15_handler);

Change-Id: I70fd780d7ebf1564a2ff7d7148411673f6de113c
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/1559
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>