Add gpio functions to sysfs and some refactoring

Functions added:

- sysfs_gpio_setvalue
- sysfs_gpio_getvalue
- sysfs_led_setvalue

Also:

- Corrected indentation in sysfs.c
- Inserted argument names in the function prototypes

Signed-off-by: Parav Nagarsheth <parav.nagarsheth@gmail.com>
Remove duplicate code from wiring_digital.c

The functions in sysfs make some of the code here redundant
Remove duplicate code from virtual_main.h

This is now shifted to sysfs.h
Fix variant.cpp and variant.h to work with bacon cape demo

Pin 7 was incorrectly labelled PWM