sysfsgpio: support broken gpio implementations

sysfsgpio: support broken gpio implementations

Change tests when reading from 'value' in sysfs from =='0' to !='1'.
This guards against broken sysfs GPIO implementations that return
non-zero for high rather than just '1' while still being clean and
correct code. Note that sysfs will never output a leading zero even
in a very broken implementation as that is covered in gpiolib.c, not
the offending driver.

Tested against broken Freescale kernel 3.14.38 on i.MX6SL.

Change-Id: Id05567bb8504b1babef33d6ee5172bceefeca8b8
Signed-off-by: Matthew Campbell <mcampbell@izotope.com>
Reviewed-on: http://openocd.zylin.com/3121
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>