pcm: Further cleanup of unused bits of the PCM ACPI:

* pcm_get_bytes_remaining()
 * pcm_calculate_peaks()
 * pcm_get_peak_buffer()

Nothing in-tree uses these at all (except for the lua plugin wrapper)

Change-Id: I971b7beed6760250c8b1ce58f401a601e1e2d585

firmware/target/arm/rk27xx/pcm-rk27xx.c

@@ -250,12 +250,6 @@ void pcm_dma_apply_settings(void)
     audiohw_set_frequency(pcm_fsel);
 }
 
-size_t pcm_get_bytes_waiting(void)
-{
-    /* current terminate count is in transfer size units (4bytes here) */
-    return (HDMA_CCNT0 & 0xffff)<<2;
-}
-
 /* audio DMA ISR called when chunk from callers buffer has been transfered */
 void INT_HDMA(void)
 {