linux-firmware: add Skylake audio firmware

This adds Skylake audio dsp firmware which will be used in Skylake systems
with adsp enabled.

The version of this firmware release is 8.20.00.669

The md5sum of this firmware binary is 039c718077ea3c3a4253110a0554f422
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

WHENCE

@@ -2830,6 +2830,16 @@ License: Redistributable. See LICENCE.fw_sst_0f28 for details
 
 --------------------------------------------------------------------------
 
+Driver: snd-soc-skl
+
+File: intel/dsp_fw_release.bin
+Version: 8.20.00.669
+md5sum: 039c718077ea3c3a4253110a0554f422
+
+License: Redistributable. See LICENCE.adsp_sst for details
+
+--------------------------------------------------------------------------
+
 Driver: smsmdtv - Siano MDTV Core module
 
 File: cmmb_vega_12mhz.inp