MFC r266937:

  Export two new settings for the AM335x PWM, the clock prescaler (clkdiv)
  and the actual PWM frequency.

  Enforce the maximum value for the period sysctl.

  The frequency systcl now allows the direct setting of the PWM frequency
  (it will try to find the better clkdiv and period for a given frequency,
  i.e. the ones that will give the better PWM resolution).

  This allows the use lower frequencies on the PWM.  Without changing the
  clock prescaler the minimum PWM frequency was 1.52kHz.

  PWM frequencies checked with an osciloscope.

  PWM output tested with some R/C servos at 50Hz.
MFC r266960:

  Configure the analog input 7 which, on BBB, is connected to the 3V3B rail
  through a voltage divisor (R163 and R164 on page 4 of BBB schematic).

  Add a note about this on ti_adc(4) man page.  The ti_adc(4) man page will
  first appear on 10.1-RELEASE.

  Suggested by: Sulev-Madis Silber (ketas)
  Manual page reviewed by:      brueffer (D127)