MFC 264052, 264057, 264065, 264094, 264103, 264120

  Actually save the mpcore clock frequency retrieved from fdt data.

  imx6..
  - Don't call sdhci_init_slot() until after handling the FDT properties
    related to detecting card presence.
  - Flag several sysctl variables as tunables.
  - Rework the cpu frequency management code for imx6 to add "operating
    points" and min/max frequency controls.

  generic timer...
  - Setup both secure and non-secure timer IRQs.
    We don't know our ARM security state, so one of them will operate.
  - Don't set frequency, since it's unpossible in non-secure state.
    Only rely on DTS clock-frequency value or get clock from timer.
MFC 264128, 264129, 264130, 264135,

  Fix TTB set operation for armv7. Perform sychronization (by "isb" barrier)
  after TTB is set.

  Fix TLB maintenance issues for armv6 and armv7.

    - Add cpu_cpwait to comply with the convention.
    - Add missing TLB invalidations, especially in pmap_kenter & pmap_kremove
      with distinguishing between D and ID pages.
    - Modify pmap init/bootstrap invalidations to ID, just to be safe.
    - Fix TLB-inv and PTE_SYNC ordering.

  Allocate per-cpu resources for doing pmap_zero_page() and pmap_copy_page().
  This is performance enhancement rather than bugfix.

  We don't support any ARM systems with an ISA bus and don't need a freelist
  of memory to support ISA addressing limitations.
MFC 264137:  Switch wandboards over to the common IMX6 kernel config, which
has SMP enabled.  Also switch IMX6 to use SCHED_ULE.
MFC 264137:  Switch wandboards over to the common IMX6 kernel config, which
has SMP enabled.  Also switch IMX6 to use SCHED_ULE.