Add clock_synchronize() which may be used to re-synchonize the system time...

Add clock_synchronize() which may be used to re-synchonize the system time with an RTC after recovering from a low power state

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@4503 42af7a65-404d-4744-a932-0658087f49c3