Math: FFT: Rename setup script function with sof prefix

The script function name and help is updated. A README.md is
added how to use it.

Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>

src/math/fft/tune/README.md

@@ -0,0 +1,9 @@
+# Export FFT twiddle factors data
+
+To generate the twiddle factors headers for FFT max size of 1024
+(current assumption) run these shell commands:
+
+octave -q --eval "sof_export_twiddle(32, 'twiddle_32.h', 1024);"
+octave -q --eval "sof_export_twiddle(16, 'twiddle_16.h', 1024);"
+cp twiddle_32.h ../../../include/sof/audio/coefficients/fft/
+cp twiddle_16.h ../../../include/sof/audio/coefficients/fft/

src/math/fft/tune/sof_export_twiddle.m

@@ -1,4 +1,4 @@
-% export_twiddle(bits, fn, fft_size_max)
+% sof_export_twiddle(bits, fn, fft_size_max)
 %
 % Input
 %   bits - Number of bits for data, 16 or 32
@@ -9,7 +9,7 @@
 %
 % Copyright (c) 2022, Intel Corporation. All rights reserved.
 
-function export_twiddle(bits, fn, fft_size_max)
+function sof_export_twiddle(bits, fn, fft_size_max)
 
 if nargin < 2
 	fn = 'twiddle.h';