Rename NMD::extract_fs_15_14_13_12_11(uint64 instruction) to
NMD::extract_fs_20_19_18_17_16(uint64 instruction).

Reviewed-by: Aleksandar Rikalo <arikalo@wavecomp.com>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>