soc/amd/stoneyridge: Add GPIO40 to GPIO list

GPIO40 is a valid GPIO for the Stoney FT4 package, so add it to the
list of GPIOs.

BUG=b:69305596
TEST=Build Kahlee & Grunt

Change-Id: I20fce60ff1a61761b907518c0a6e1685a17f2886
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/22658
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Marc Jones <marc@marcjonesconsulting.com>

src/soc/amd/stoneyridge/include/soc/gpio.h

@@ -61,6 +61,7 @@
 #define GPIO_25				25
 #define GPIO_26				26
 #define GPIO_39				39
+#define GPIO_40				40
 #define GPIO_42				42
 
 /* GPIO_64 - GPIO_127 */