imx: imx7d: clock control module support

imx: imx7d: clock control module support

* Add Clock control module (CCM) support
* iMX7D SoC introduces 3 main clock sysmtem abstraction for clock
  root frequency generation denominated clock slices.
  Core clock slice: hihg speed clock for ARM core
  Bus clock slice: for bus clocks
  IP clock slice: Peripheral clocks
* At system boot ROM enables PLL_ARM, PLL_DDR, PLL_SYS, PLL_ENET
  In u-boot, we have to:
  - Configure PFD3- PFD7 for freq we needed in u-boot
  - Set clock root for peripherals (ip channel)

Signed-off-by: Adrian Alonso <aalonso@freescale.com>
Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Signed-off-by: Ye.Li <B37916@freescale.com>