soc/intel/skylake: Add function for gpio_t to ACPI pin translation

Add the function defined in gpio.h to translate a gpio_t into a
value for use in an ACPI GPIO pin table.

For skylake this just returns the gpio_t value as the pins are
translated directly and they are all in the same ACPI device.

Change-Id: I00fad1cafec2f2d63dce9f7779063be0532649c7
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/15520
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/skylake/gpio.c

@@ -408,3 +408,8 @@ const char *gpio_acpi_path(gpio_t gpio_num)
 {
 	return "\\_SB.PCI0.GPIO";
 }
+
+uint16_t gpio_acpi_pin(gpio_t gpio_num)
+{
+	return gpio_num;
+}