ARM: imx: clk-vf610: define PLL's clock tree

So far, the required PLL's (PLL1/PLL2/PLL5) have been initialized
by boot loader and the kernel code defined fixed rates according
to those default configurations. Beginning with the USB PLL7 the
code started to initialize the PLL's itself (using imx_clk_pllv3).

However, since commit dc4805c2


(ARM: imx: remove ENABLE and BYPASS bits from clk-pllv3 driver)
imx_clk_pllv3 no longer takes care of the ENABLE and BYPASS bits,
hence the USB PLL were not configured correctly anymore.

This patch not only fixes those USB PLL's, but also makes use of
the imx_clk_pllv3 for all PLL's and alignes the code with the PLL
support of the i.MX6 series.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>