it83xx: gpio: Set KSO/KSI pins to GPIO mode by gpio_set_flags_by_mask
it83xx: gpio: Set KSO/KSI pins to GPIO mode by gpio_set_flags_by_mask

With this change, we can reconfigure KSO/KSI pins as GPIO mode
by calling gpio_set_flags_by_mask().

BUG=b:111006203
BRANCH=none
TEST=Declare KSO/KSI signal with GPIO_INPUT flag and check if
     these pins work as GPIO input.

Change-Id: I3b1fcc989745da08898d2f254dedc9655fd0ef83
Signed-off-by: Dino Li <338d523ecf3700bd86eb9c34d220f91911d2a18c@ite.com.tw>
Reviewed-on: https://chromium-review.googlesource.com/1163584
Reviewed-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec