drivers: clk: agilex5: Set PLL to asynchronous mode

drivers: clk: agilex5: Set PLL to asynchronous mode

PLL frequency would overshoot from the original target in
synchronous mode during low VCC voltage condition.

To resolve this issue, PLL is set to run on asynchronous mode
instead of enabling synchronous mode in the clock driver.

Signed-off-by: Muhammad Hazim Izzat Zamri <muhammad.hazim.izzat.zamri@altera.com>
Signed-off-by: Alif Zakuan Yuslaimi <alif.zakuan.yuslaimi@altera.com>
Reviewed-by: Tien Fong Chee <tien.fong.chee@altera.com>