irqchip/loongson-pch-pic: Move find_pch_pic() into CONFIG_ACPI

MIPS doesn't declare find_pch_pic(), which makes a build warning:

>> drivers/irqchip/irq-loongson-pch-pic.c:51:5: warning: no previous prototype for function 'find_pch_pic' [-Wmissing-prototypes]
   int find_pch_pic(u32 gsi)
       ^
   drivers/irqchip/irq-loongson-pch-pic.c:51:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   int find_pch_pic(u32 gsi)
   ^
   static
   1 warning generated.

Move find_pch_pic() into CONFIG_ACPI which only used by LoongArch to fix
the warning.

BTW, remove the duplicated declaration of find_pch_pic() in irq.h.
Reported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NHuacai Chen <chenhuacai@loongson.cn>
Signed-off-by: NMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220808093205.3658485-1-chenhuacai@loongson.cn

arch/loongarch/include/asm/irq.h

@@ -81,7 +81,6 @@ extern struct acpi_vector_group msi_group[MAX_IO_PICS];
 #define GSI_MIN_PCH_IRQ		LOONGSON_PCH_IRQ_BASE
 #define GSI_MAX_PCH_IRQ		(LOONGSON_PCH_IRQ_BASE + 256 - 1)
 
-extern int find_pch_pic(u32 gsi);
 extern int eiointc_get_node(int id);
 
 struct acpi_madt_lio_pic;

drivers/irqchip/irq-loongson-pch-pic.c

@@ -48,25 +48,6 @@ static struct pch_pic *pch_pic_priv[MAX_IO_PICS];
 
 struct fwnode_handle *pch_pic_handle[MAX_IO_PICS];
 
-int find_pch_pic(u32 gsi)
-{
-	int i;
-
-	/* Find the PCH_PIC that manages this GSI. */
-	for (i = 0; i < MAX_IO_PICS; i++) {
-		struct pch_pic *priv = pch_pic_priv[i];
-
-		if (!priv)
-			return -1;
-
-		if (gsi >= priv->gsi_base && gsi < (priv->gsi_base + priv->vec_count))
-			return i;
-	}
-
-	pr_err("ERROR: Unable to locate PCH_PIC for GSI %d\n", gsi);
-	return -1;
-}
-
 static void pch_pic_bitset(struct pch_pic *priv, int offset, int bit)
 {
 	u32 reg;
@@ -325,6 +306,25 @@ IRQCHIP_DECLARE(pch_pic, "loongson,pch-pic-1.0", pch_pic_of_init);
 #endif
 
 #ifdef CONFIG_ACPI
+int find_pch_pic(u32 gsi)
+{
+	int i;
+
+	/* Find the PCH_PIC that manages this GSI. */
+	for (i = 0; i < MAX_IO_PICS; i++) {
+		struct pch_pic *priv = pch_pic_priv[i];
+
+		if (!priv)
+			return -1;
+
+		if (gsi >= priv->gsi_base && gsi < (priv->gsi_base + priv->vec_count))
+			return i;
+	}
+
+	pr_err("ERROR: Unable to locate PCH_PIC for GSI %d\n", gsi);
+	return -1;
+}
+
 static int __init
 pch_lpc_parse_madt(union acpi_subtable_headers *header,
 		       const unsigned long end)