Remove wrong arch name from in arm64/autoconf.c

Don't change it to arm64. Just get rid of it.
Rework and improve interrupts handling on ARM64

Clarify namespace
  - arm_ for general calls that could be implemented and exported by
    both architecture variants (64bit and 32bit)
  - arm64_ for specific structures and variables that may differ
  - get rid of cpu_ prefix derived from mips
  - make the names more straightforward (bus_setup_ calls arm_setup_, etc.)

Implement missing interrupts management routines, rework old ones
  - Implement teardown and config methods
  - Maintain table of dynamicaly allocated structures that describe each
    interrupt
  - Add locking
  - Reimplement all functions to get proper interrupts handling
  - Minor fixes to types, etc.

Fix issue with reversed order of interrupt parrent - child attachment
  - It is now possible to call bus_setup_interrupt before appropriate
    PIC is attached. Interrupts and handlers are configured during cold
    boot and in configure_final() the interrupts are actually enabled.

Adjust nexus routines
  - Call arm_setup_intr() once per bus_setup_intr() call
    - Don't forget to activate resource before using it
    - Resource start and end will not differ for BUS_RES_IRQ
      type resource. In addition this will override cookie parameter
      what will make related irq handler impossible to release.

Adjust GICv1/2 driver to use new PIC registeration method
Add interrupt statistics handling for ARM64. Remove them from exceptions.S
Add dummy arm_register_pic() routine to ARM to stay aligned with ARM64

This will partially fix the GICv1/2 compilation for ARM
Further clean-up of ARM64's exception.S
Add proper (C) to ARM64's intr_machdep.c.

Old (C) do not apply anymore since this file has more in common
with powerpc/intr_machdep.c now.