ARM: dts: hummingboard: Setup pwm lines

Setup pwm lines as follows -
pwm1: In case HummingBoard base carrier; this pin drives through a serial
      capacitor the mono out of the audio jack.
      In case HummingBoard pro the this pad can be reached by wiring to
      C8 capacitors on the board.
pwm2: Setup pwm2 on gpio-1 but leave the default function of the iopad as
      a gpio.
      The user can change the io pad mux in user space and therefore use
      this function on gpio-1 (pin number 7 on the 26 pin header).

pwm3,pwm4: unused

Signed-off-by: Rabeeh Khoury <rabeeh@solid-run.com>