Remove unnecessary includes and an unused softc variable.  While here apply
two minor style(9) fixes.

Approved by:	adrian (mentor)
Move the GPIOBUS_SET_PINFLAGS(..., ..., pin, GPIO_PIN_OUTPUT) to led(4)
control callback function.  This makes gpioled(4) works even if the pin
is accidentally set to an input.

Approved by:	adrian (mentor)
Fix the pin value reading on AM335x.  Because of the inverted logic it was
always returning '0' for all the reads, even for the outputs.  It is now
known to work with gpioiic(4) and gpioled(4).

Approved by:	adrian (mentor)
Tested on:	BBB