gale: add dev switch back as physical presence GPIO

gale has a button which is essentially used as a
"physical presence" button.  Its only use is to emulate
^D or ^U on boot when the button is pressed.
(See depthcharge src/board/gale/board.c)

Previously (and currently in CrOS firmware branch) this
GPIO was defined as the physical developer switch,
and read as such in depthcharge.  It was removed in
cleanup patch CB:18980.

Add the GPIO back as physical presence ("presence"),
which will be read by depthcharge in CL:1532492.

BUG=b:124141368, b:124192753, chromium:942901
TEST=util/lint/checkpatch.pl -g origin/master..HEAD
TEST=util/abuild/abuild -B -e -y -c 50 -p none -x
TEST=make clean && make test-abuild
BRANCH=none

Change-Id: Ic144f839b7f9933d573db8f84c4bf5905eea96f6
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/31993
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

src/mainboard/google/gale/chromeos.c

@@ -24,6 +24,8 @@
 #include <timer.h>
 #include <vendorcode/google/chromeos/chromeos.h>
 
+#define PP_SW   41
+#define PP_POL  ACTIVE_LOW
 #define REC_POL ACTIVE_LOW
 #define WP_POL  ACTIVE_LOW
 
@@ -68,6 +70,7 @@ static int read_gpio(gpio_t gpio_num)
 void fill_lb_gpios(struct lb_gpios *gpios)
 {
 	struct lb_gpio chromeos_gpios[] = {
+		{PP_SW, PP_POL, read_gpio(PP_SW), "presence"},
 		{get_rec_sw_gpio_pin(), REC_POL,
 			read_gpio(get_rec_sw_gpio_pin()), "recovery"},
 		{get_wp_status_gpio_pin(), WP_POL,