intel_edison_fab_c.c: Remove dependency on debugfs

intel_edison_fab_c.c: Remove dependency on debugfs

The MRAA library needs the debugfs interface in order to access GPIO
pin modes attributes. Mounting the debugfs is not always desirable so this
patch instructs libmraa to first check for the required attributes in
the normal SYSFS CLASS GPIO interface and to use debugfs as a fallback.

Signed-off-by: Mihai Serban <mihai.serban@intel.com>
Signed-off-by: Constantin Musca <constantin.musca@intel.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>