mb/intel/apollolake_rvp: do UART pad configuration at board-level

UART pad configuration should not be done in common code, because that
may cause short circuits, when the user sets a wrong UART index. Thus,
add the corresponding pads to a early UART gpio table for the board as
a first step. Common UART pad config code then gets dropped in CB:48829.

Also switch to `bootblock_mainboard_early_init` to configure the pads in
early bootblock before console initialization, to make the console work
as early as possible. The board does not do any other gpio configuration
in bootblock, so this should not influence behaviour in a negative way
(e.g. breaking overrides).

Change-Id: Id6b55d7f3d3fbfc5b55497708f24006614760d03
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49434
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/intel/apollolake_rvp/Makefile.inc

@@ -1 +1 @@
-#Nothing here yet
+bootblock-y += bootblock.c

src/mainboard/intel/apollolake_rvp/bootblock.c

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <bootblock_common.h>
+#include <soc/gpio.h>
+
+#include "gpio.h"
+
+void bootblock_mainboard_early_init(void)
+{
+	gpio_configure_pads(early_gpio_table, ARRAY_SIZE(early_gpio_table));
+}

src/mainboard/intel/apollolake_rvp/gpio.h

@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <soc/gpio.h>
+
+static const struct pad_config early_gpio_table[] = {
+	PAD_CFG_NF(GPIO_46, NATIVE, DEEP, NF1),	/* UART2 RX */
+	PAD_CFG_NF(GPIO_47, NATIVE, DEEP, NF1),	/* UART2 TX */
+};