ASoC: rockchip: Kconfig: Remove unused PREALLOC_BUFFER_SIZE

This reverts part of commit 213457f
("ASoC: rockchip: pcm: Adjust min/max value for pcm config").

Instead, pass module option 'prealloc_buffer_size_kbytes'
to specify it. any details please refer to:
Documentation/sound/alsa-configuration.rst

e.g. 32 kbytes prealloc buffer size:

"snd_soc_core.prealloc_buffer_size_kbytes=32"

Change-Id: I3788620807c4e94d3e9c15ef224b76266722dcc1
Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>

sound/soc/rockchip/Kconfig

@@ -6,14 +6,6 @@ config SND_SOC_ROCKCHIP
 	  the Rockchip SoCs' Audio interfaces. You will also need to
 	  select the audio interfaces to support below.
 
-config SND_SOC_ROCKCHIP_PREALLOC_BUFFER_SIZE
-	int "Default prealloc buffer size (kbytes)"
-	depends on SND_SOC_ROCKCHIP
-	default "512"
-	help
-	  The default value is 512 kilobytes. Only change this if you know
-	  what you are doing.
-
 config SND_SOC_ROCKCHIP_AUDIO_PWM
 	tristate "Rockchip Audio PWM Driver"
 	depends on CLKDEV_LOOKUP && SND_SOC_ROCKCHIP