Revert "drivers/misc/ti-st: remove gpio handling"

This reverts commit eccf2979.

The reason is that it broke TI WiLink shared transport on Panda.
Also, callback functions should not be added to board files anymore,
so revert to implementing the power functions in the driver itself.

Additionally, changed a variable name ('status' to 'err') so that this
revert compiles properly.

Cc: stable <stable@vger.kernel.org> [3.7]
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>