MIPS: Fix build error when SMP is used without GIC

The MIPS_GIC_IPI should only be selected when MIPS_GIC is also
selected, otherwise it results in a compile error. smp-gic.c uses some
functions from include/linux/irqchip/mips-gic.h like
plat_ipi_call_int_xlate() which are only added to the header file when
MIPS_GIC is set. The Lantiq SoC does not use the GIC, but supports SMP.
The calls top the functions from smp-gic.c are already protected by
some #ifdefs

The first part of this was introduced in commit 72e20142 ("MIPS:
Move GIC IPI functions out of smp-cmp.c")
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: stable@vger.kernel.org # v3.15+
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12774/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -2169,7 +2169,7 @@ config MIPS_MT_SMP
 	select CPU_MIPSR2_IRQ_VI
 	select CPU_MIPSR2_IRQ_EI
 	select SYNC_R4K
-	select MIPS_GIC_IPI
+	select MIPS_GIC_IPI if MIPS_GIC
 	select MIPS_MT
 	select SMP
 	select SMP_UP
@@ -2267,7 +2267,7 @@ config MIPS_VPE_APSP_API_MT
 config MIPS_CMP
 	bool "MIPS CMP framework support (DEPRECATED)"
 	depends on SYS_SUPPORTS_MIPS_CMP && !CPU_MIPSR6
-	select MIPS_GIC_IPI
+	select MIPS_GIC_IPI if MIPS_GIC
 	select SMP
 	select SYNC_R4K
 	select SYS_SUPPORTS_SMP
@@ -2287,7 +2287,7 @@ config MIPS_CPS
 	select MIPS_CM
 	select MIPS_CPC
 	select MIPS_CPS_PM if HOTPLUG_CPU
-	select MIPS_GIC_IPI
+	select MIPS_GIC_IPI if MIPS_GIC
 	select SMP
 	select SYNC_R4K if (CEVT_R4K || CSRC_R4K)
 	select SYS_SUPPORTS_HOTPLUG_CPU
@@ -2306,6 +2306,7 @@ config MIPS_CPS_PM
 	bool
 
 config MIPS_GIC_IPI
+	depends on MIPS_GIC
 	bool
 
 config MIPS_CM