audio: MMAP NOIRQ mode shareable file descriptor

Derive a shareable file descriptor for the DMA buffer
used for MMAP NOIRQ

Bug: 37167970
Test: run AAudio CTS tests with MMAP enabled
Change-Id: Ibdd633fad35ed397f6de746e5755a02522e39777
diff --git a/hal/msm8960/platform.c b/hal/msm8960/platform.c
index 53838a7..50c6490 100644
--- a/hal/msm8960/platform.c
+++ b/hal/msm8960/platform.c
@@ -1200,3 +1200,9 @@
     }
     return 0;
 }
+
+int platform_get_mmap_data_fd(void *platform __unused, int fe_dev __unused, int dir __unused,
+                              int *fd __unused, uint32_t *size __unused)
+{
+    return -ENOSYS;
+}