remove mmap capability from amazon mt8163 pcm audio driver

For reasons known only to MediaTek, the pcm driver used by most amazon devices
of this era provide a fake zero page address whenever a mmap is attempted.
Naturally, this causes a kernel panic when an audio server like pulseaudio
attempts to mmap the sound device using the fake address. Remove this dummy
page function and remove mmap flags from the driver description so pulse
handles the device correctly.

Verified on amazon-biscuit (Echo Dot 2G) but may also apply to other MT8163
devices like karnak and douglas. MT8127 devices like ford appear to pull this
dummy page trick as well, so a modified patch may work there.
diff --git a/sound/soc/mediatek/mt_soc_audio_8163_amzn/mt_soc_pcm_dl1_i2s0Dl1.c b/sound/soc/mediatek/mt_soc_audio_8163_amzn/mt_soc_pcm_dl1_i2s0Dl1.c
index b68f2fa..afaaba8 100644
--- a/sound/soc/mediatek/mt_soc_audio_8163_amzn/mt_soc_pcm_dl1_i2s0Dl1.c
+++ b/sound/soc/mediatek/mt_soc_audio_8163_amzn/mt_soc_pcm_dl1_i2s0Dl1.c
@@ -124,8 +124,7 @@ static const struct snd_kcontrol_new Audio_snd_I2S0dl1_controls[] = {
 
 static struct snd_pcm_hardware mtk_I2S0dl1_hardware = {
 
-	.info = (SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_INTERLEAVED |
-		SNDRV_PCM_INFO_RESUME | SNDRV_PCM_INFO_MMAP_VALID),
+	.info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_RESUME),
 	.formats = SND_SOC_ADV_MT_FMTS,
 	.rates = SOC_HIGH_USE_RATE,
 	.rate_min = SOC_HIGH_USE_RATE_MIN,
@@ -1125,15 +1125,6 @@ static int mtk_pcm_I2S0dl1_silence(struct snd_pcm_substream *substream,
 	return 0;
 }

-static void *dummy_page[2];
-
-static struct page *mtk_I2S0dl1_pcm_page(struct snd_pcm_substream *substream,
-	unsigned long offset)
-{
-	pr_debug("%s\n", __func__);
-	return virt_to_page(dummy_page[substream->stream]);
-}
-
 static int mtk_I2S0dl1_reboot(struct notifier_block *nb,
 	unsigned long action, void *data)
 {
@@ -908,7 +899,6 @@ static struct snd_pcm_ops mtk_I2S0dl1_ops = {
 	.pointer = mtk_pcm_I2S0dl1_pointer,
 	.copy = mtk_pcm_I2S0dl1_copy,
 	.silence = mtk_pcm_I2S0dl1_silence,
-	.page = mtk_I2S0dl1_pcm_page,
 };
 
 static struct snd_soc_platform_driver mtk_I2S0dl1_soc_platform = {
