clk: imx: pllv3: support fractional multiplier on vf610 PLL1/PLL2

On vf610, PLL1 and PLL2 have registers to configure fractional part of
frequency multiplier.

This patch adds support for these registers.

This fixes "fast system clock" issue on boards where bootloader sets
fractional multiplier for PLL1.

Suggested-by: Andrey Smirnov <andrew.smirnov@gmail.com>
CC: Chris Healy <cphealy@gmail.com>
Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Tested-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>