dts: mpc512x: add clock related device tree specs

this addresses the clock driver aka provider's side of clocks
- introduce a 'clocks' subtree with an 'osc' node for the crystal
  or oscillator SoC input (fixed frequency)
- the 'clock@f00' clock-control-module node references the 'osc' for
  its input, and is another provider for all the clocks which the
  CCM component manages
- prepare for future references to clocks from peripheral nodes
  by means of the <&clks ID> syntax and symbolic ID names which a
  header file provides
- provide default values with 33MHz oscillator frequency in the
  common include (the 66MHz IPS bus already was there), and add
  override values for the ifm AC14xx board which deviates from
  the reference design (25MHz xtal, 80MHz IPS bus)

Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: devicetree@vger.kernel.org
Reviewed-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Gerhard Sittig <gsi@denx.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>