audio HAL: add support for MMAP IRQ mode streams.

Introduce MMAP NOIRQ in shared mode.

CRs-Fixed: 2071843
Change-Id: I79ee079475d23f01aaf730a488b79831fd070df1
diff --git a/hal/msm8974/platform.h b/hal/msm8974/platform.h
index 06f2cdc..33edf75 100644
--- a/hal/msm8974/platform.h
+++ b/hal/msm8974/platform.h
@@ -385,6 +385,8 @@
 #define EC_REF_RX "I2S_RX"
 #else
 #define LOWLATENCY_PCM_DEVICE 15
+#define MMAP_PLAYBACK_PCM_DEVICE 18
+#define MMAP_RECORD_PCM_DEVICE 18
 #define EC_REF_RX "SLIM_RX"
 #endif