ASoC: xilinx: Standardize ASoC menu

Current Kconfig menu at [ALSA for SoC audio support] has no rules.
So, some venders are using menu style, some venders are listed each drivers
on top page, etc. It is difficult to find target vender and/or drivers
because it is very random.

Let's standardize ASoC menu

Signed-off-by: Kuninori Morimoto <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

sound/soc/xilinx/Kconfig

···
 # SPDX-License-Identifier: GPL-2.0-only
+menu "Xilinx"
+
 config SND_SOC_XILINX_I2S
 	tristate "Audio support for the Xilinx I2S"
 	help
···
 	  Select this option to enable Xilinx SPDIF Audio.
 	  This provides playback and capture of SPDIF audio in
 	  AES format.
+
+endmenu