ARM: imx: pllv3: add shift for frequency multiplier

Add shift capabilties for the frequency multiplier (DIV_SELECT) to
support Vybrid's USB PLL oddity. The PLL3 and PLL7 are the only
PLL control registers which have the DIV_SELECT bit shifted by
one. Be aware, there are known documentation errors in the
reference manual too.

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