soc/intel/mtl/acpi/gpio.asl: fix missing gpio.h include

This change fixes building NovaCustom V540TU, which previously errored
out due to missing MISCCFG_GPIO_PM_CONFIG_BITS definition.

Replace soc/gpio_defs.h with gpio.h which includes everything we need,
same as it was done for ADL in change 71266, and other SoCs.

TEST=Build and boot NovaCustom V540TU

Change-Id: I52a495f696258fc63752dd8e66e318e144bb768e
Signed-off-by: Michał Kopeć <michal.kopec@3mdeb.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82674
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Reviewed-by: Krystian Hebel <krystian.hebel@3mdeb.com>
Reviewed-by: Michał Żygowski <michal.zygowski@3mdeb.com>

src/soc/intel/meteorlake/acpi/gpio.asl

@@ -1,5 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
-#include <soc/gpio_defs.h>
+#include <gpio.h>
 #include <soc/intel/common/acpi/gpio.asl>
 #include <soc/intel/common/block/acpi/acpi/gpio_op.asl>
 #include <soc/irq.h>