rbcodec dsp: Move dsp_sample_io_configure() to its own file

Makes dsp_sample_input.c a bit less messy, and dependencies
are more explicit. There's possibly a minor loss of inlining
but it isn't a big deal.

Change-Id: I30f923a0ca758f2b113d32852d1f65586dff0cd1

lib/rbcodec/platform.h

@@ -41,6 +41,11 @@ size_t strlcpy(char *dst, const char *src, size_t siz);
 #ifndef INIT_ATTR
 # define INIT_ATTR
 #endif
+
+#ifndef INITDATA_ATTR
+# define INITDATA_ATTR
+#endif
+
 /*
 #ifdef CODEC