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

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.

git-svn-id: svn://svn.freebsd.org/base/stable/10@266352 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f