Tweak opus build flags and allocs

This gets us to ~40% of one core cpu usage during playback. Good enough
for a while I reckon!

Paid for the internal ram usage by reclaiming some stack size headroom.

lib/opusfile/include/custom_support.h

@@ -6,12 +6,10 @@
 #define OVERRIDE_OPUS_ALLOC
 #define OVERRIDE_OPUS_FREE
 
-static OPUS_INLINE void *opus_alloc (size_t size)
-{
-   return heap_caps_malloc(size, MALLOC_CAP_SPIRAM);
+static OPUS_INLINE void* opus_alloc(size_t size) {
+  return heap_caps_malloc(size, MALLOC_CAP_INTERNAL | MALLOC_CAP_8BIT);
 }
 
-static OPUS_INLINE void opus_free (void *ptr)
-{
-   heap_caps_free(ptr);
+static OPUS_INLINE void opus_free(void* ptr) {
+  heap_caps_free(ptr);
 }