soc/intel/xeon_sp/cpx: remove unused gpio.h

This file does not contain useful information and is not used to build
the image. The common GPIO driver from soc/intel/common uses layout in
lewisburg_pch_gpio_defs.h [1,2] file, which is correct for all chipsets
from the Lewisburg family: C621, C621A, C622, C624, C625, C626, C627,
C627A, C628, C629, C629A [3]

[1] src/soc/intel/xeon_sp/include/soc/lewisburg_pch_gpio_defs.h
[2] https://review.coreboot.org/c/coreboot/+/39425
[3] Intel document #547817

Change-Id: I1f3ac4afff9e628890df8cec075fd3e42a590172
Signed-off-by: Maxim Polyakov <max.senia.poliak@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43535
Reviewed-by: Jonathan Zhang <jonzhang@fb.com>
Reviewed-by: Andrey Petrov <andrey.petrov@gmail.com>
Reviewed-by: Bryant Ou <bryant.ou.q@gmail.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/xeon_sp/cpx/include/soc/gpio.h

@@ -1,11 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-
-/* not implemented, adding defaults just to make common code happy */
-
-#ifndef _SOC_GPIO_H_
-#define _SOC_GPIO_H
-
-#define GPIO_NUM_PAD_CFG_REGS		0
-#define NUM_GPI_STATUS_REGS		0
-
-#endif