soc: samd5x: xosc32: Correct oscillator start up time to not used reserved value

[nandojve]

Describe the bug
The current Atmel samd5x SoC series have a fixed startup time which is not suitable for all situations. This oscillator is used as source to main clock PLL and system may fail to boot due to wrong configuration.

Expected behavior
Customers can select correct xosc32 startup time.

Impact
Board may not boot.

[dkalowsk]

Thanks for this!

[nandojve]

Content got merged.