arm: airoha: introduce EN7523 helpers to get SCU and CHIP_SCU regmaps

We need access SCU and CHIP_SCU regmaps in several places (clk-airoha,
reset-airoha, airoha_eth). Unfortunately these regmaps can't be easily
retrieved with a common code, because of different Airoha SoCs uses
a different dts structure.

To make life easy we can write a commonly named SoC specific helpers
for these tasks. This patch implements helpers for Airoha EN7523 SoC.

Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu>

arch/arm/include/asm/arch-en7523

@@ -0,0 +1 @@
+arch-airoha

arch/arm/mach-airoha/en7523/Makefile

@@ -1,3 +1,4 @@
 # SPDX-License-Identifier:	GPL-2.0
 
 obj-y += init.o
+obj-y += scu-regmap.o

arch/arm/mach-airoha/en7523/scu-regmap.c

@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Author: Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu>
+ */
+
+#include <dm/ofnode.h>
+#include <linux/err.h>
+#include <asm/arch/scu-regmap.h>
+
+static struct regmap *airoha_scu_node_regmap_by_index(unsigned int index)
+{
+	struct regmap *map;
+	ofnode node;
+	int err;
+
+	node = ofnode_by_compatible(ofnode_null(), "airoha,en7523-scu");
+	if (!ofnode_valid(node))
+		return ERR_PTR(-EINVAL);
+
+	/* CHIP_SCU (index=0), SCU (index=1) */
+	err = regmap_init_mem_index(node, &map, index);
+	if (err)
+		return ERR_PTR(err);
+
+	return map;
+}
+
+struct regmap *airoha_get_scu_regmap(void)
+{
+	/* CHIP_SCU (index=0), SCU (index=1) */
+	return airoha_scu_node_regmap_by_index(1);
+}
+
+struct regmap *airoha_get_chip_scu_regmap(void)
+{
+	/* CHIP_SCU (index=0), SCU (index=1) */
+	return airoha_scu_node_regmap_by_index(0);
+}