testing/openocd: enable sysfsgpio configure option

The release notes for 0.10.0 explicitly request this [0]:

	7. Please add --enable-sysfsgpio for all targets running Linux, the
	kernel (esp. useful for SBCs), additionally for builds that support
	RaspberryPi, please add --enable-bcm2835gpio

[0]: https://sourceforge.net/p/openocd/mailman/message/35570895/