This patch adds puv3 gpio (General Purpose Input/Output) support,
include gpio device simulation and its interrupt support.

v1->v2: Add initialization to ret in puv3_gpio_read.
Signed-off-by: NGuan Xuetao <gxt@mprc.pku.edu.cn>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>