hal: Restrict SSR recording to channel position representation

Surround Sound Recording(SSR) supports only channel position
representation while default channel mask for multi-channel
recording is always index representation.
Return updated channel mask in case index representation is sent
for channel count 6. This ensures audio flinger reopens the session
with updated position representation channel mask.
And also handled the case if any client requests recording with
multichannel when SSR is not enabled, will check the max_mic_count
supported by the device and update the channel mask accordingly.

Change-Id: Ib925a5f31d50182cd595e547f3412ed809224a5a
diff --git a/hal/platform_api.h b/hal/platform_api.h
index 7bd6756..c3b76b0 100644
--- a/hal/platform_api.h
+++ b/hal/platform_api.h
@@ -178,4 +178,5 @@
     void* data, int* length);
 
 unsigned char* platform_get_license(void* platform, int* size);
+int platform_get_max_mic_count(void *platform);
 #endif // AUDIO_PLATFORM_API_H