add pin configuration structure for PWM

pin configuration structure holds the information like file descriptor - enable and duty_cycle files  and PWM number in sysfs corresponding to arduino pin number.
add pinstat - shows functionality of pin

PinState structure is useful to check if current pin is used as pwm or input
disable cap manager function of Beaglebone

Cap manager is no longer required for CFA10036
add function digitalPinhasPWM

This function determines if given arduino pin has PWM or not
change method to initialize PWM in variant.cpp file
include libraries and define PWM time period constant

also add name of the author
update pwmExport function

takes pwm enable and duty_cycle file descriptor as arguments and returns status or failure of export
add sysfsPwnEnable function

It is used to turn on PWM chnnnel corresponds to arduino pin number.
add sysfsPwmDisable function

It is used to turn off the PWM channel corresponds to arduino pin number
add PWM directory

add PWM directory: /sys/class/pwm/pwmchip0
add pin2Pwmhandler function for PWM enable and duty_cycle

These function will return file descriptor of enable and duty_cycle file of PWM.
update analogWrite function

Instead of writing 1 directly to /sys/pwm/pwmchip0/pwmx/enable, this function will use sysfsEnable function.
It will return 0 on success and -1 on failure.
Handling of file descriptor of /enable and /duty_cycle is also important. Based on mux value, appropriate functionality of pin is chosen.
add pwmInit() function

This function will export PWM channels to sysfs.