feat(mt8188): add audio support

For MT8188, MTK_AUDIO_SMC_OP_DOMAIN_SIDEBANDS is required for normal
mode switch.
  - Add audio common code and chip specific code.
  - Add new id (MTK_SIP_AUDIO_CONTROL) to mtk_sip_def.h.
  - Enable for MT8188.

Change-Id: Iff4680cd0b520b2b519ecf30ecafe100f147cc62
diff --git a/plat/mediatek/include/mtk_sip_def.h b/plat/mediatek/include/mtk_sip_def.h
index 907f0c1..2039017 100644
--- a/plat/mediatek/include/mtk_sip_def.h
+++ b/plat/mediatek/include/mtk_sip_def.h
@@ -14,6 +14,7 @@
 	_func(MTK_SIP_KERNEL_MSDC, 0x273) \
 	_func(MTK_SIP_VCORE_CONTROL, 0x506) \
 	_func(MTK_SIP_IOMMU_CONTROL, 0x514) \
+	_func(MTK_SIP_AUDIO_CONTROL, 0x517) \
 	_func(MTK_SIP_APUSYS_CONTROL, 0x51E) \
 	_func(MTK_SIP_DP_CONTROL, 0x523) \
 	_func(MTK_SIP_KERNEL_GIC_OP, 0x526)