gpio: update gpio Chinese documentation

Since the GENERIC_GPIO has been removed and the documentation of it
has been modified, this patch updates the corresponding documentation of
gpio in Chinese.

Signed-off-by: Chen Baozi <baozich@gmail.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>