us_ticker: - extarct for check rtc overflow - make common_rtc_32bit_ticks_get safe against preemption.
us_ticker: - extarct for check rtc overflow - make common_rtc_32bit_ticks_get safe against preemption.

j-greffe/mbed-os,j-greffe/mbed-os,j-greffe/mbed-os,j-greffe/mbed-os,j-greffe/mbed-os,j-greffe/mbed-os