ARM: imx: pll1_sys should be an initial on clk

We always boot from PLL1, so let's have pll1_sys in the clks_init_on
list to have clk prepare/enable use count match the hardware status,
so that drivers managing pll1_sys like cpufreq can get the use count
right from the start.

Reported-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>