MFC 265440, 265441, 265444, 265445, 265446, 265447:

MFC 265440, 265441, 265444, 265445, 265446, 265447:

  Move the pl310.enabled tunable to hw.pl310.enabled.  Clean up a few minor
  style(9) nits.  Use DEVMETHOD_END.

  Break out the code that figures out the L2 cache geometry to its own
  routine, so that it can be called from multiple places in upcoming changes.

  Call platform_pl310_init() before enabling the controller, and handle the
  case where the controller is already enabled.

  Add defines for the bits in the PL310 debug control register.

  Add a public routine to set the L2 cache ram latencies.  This can be
  called by platform init routines to fine-tune cache performance.

  Enable PL310 power-saving modes and tune the cache ram latencies for imx6.

git-svn-id: svn://svn.freebsd.org/base/stable/10@266384 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f