Add SYSCLK calibration method to select the calibration value with minimum error

[dhineshkumarmcci]

Add the system clock calibration value which has minimum error. Working on reference with the App note from STMicro.
https://www.st.com/content/ccc/resource/technical/document/application_note/32/b2/1a/19/3e/f9/4b/d0/DM00150625.pdf/files/DM00150625.pdf/jcr:content/translations/en.DM00150625.pdf