MFC r262534, r262548, r262549, r262552, r262568, r262581, r262583, r262584,
    r262585, r262587, r262696, r262712

  Replace many pasted identical definitions of cpu_initclocks() with a common
  implementation in arm/machdep.c.

  aicasm: Don't complain about missing prototypes to ease bootstrap issues.

  Vybrid: Add driver for Inter-Integrated Circuit (I2C).

  imx6: Initialize the Low Power Mode bits to keep the ARM cores running
  during WFI.

  All our current ARM multi-core systems have all cores in one package with
  a shared L2 cache, reflect that in the common cpu_topo() routine.

  mpcore timer: Supply a DELAY() implementation via weak linkage, so that
  SoC-specific code can supply a better implementation.

  imx6: Add some rudimentary voltage control.

  Add an armv7 implementation of cpu_sleep().

  Add __used attribute so that the DELAY implementation doesn't get
  optimized away as unreferenced, causing linker errors when trying to
  resolve the weak reference to the missing function.