MFC r336094, r336096

r336094:
Catch up with improvements in RTC handling... It's no longer necessary to
ignore the timestamp passed in to settime() due to inaccuracy, the core
routines now pass in a nanosecond-accurate time freshly-obtained before
calling each driver's settime() method. Also, add calls to the new
debugging output helpers.

r336096:
Make the imx6_snvs driver usable as a module, add pnp info. Add a manpage.