MLK-10091 arm: imx: check pll1 enable when changing arm_podf

According to the hardware design, when changing the arm_podf divider,
make sure the pll1 has clk output. If the pll1 output is disabled before
changing the arm_podf, enbale and bypass the pll1 to make sure the
arm_podf can be successfully changed.

Signed-off-by: Bai Ping <b51503@freescale.com>