ASoC: mediatek: mt2701: add HDMI audio memif, FE and BE DAIs

ASoC: mediatek: mt2701: add HDMI audio memif, FE and BE DAIs

Extend the MT2701/MT7623N AFE driver with the HDMI playback path:

  - a new HDMI DMA memif (MT2701_MEMIF_HDMI) mapped to the
    AFE_HDMI_OUT_{CON0,BASE,CUR,END} registers;
  - a PCM_HDMI front-end DAI (S16_LE only, 44.1k/48k) which feeds
    the memif via DPCM;
  - an HDMI BE DAI wrapping the AFE_8CH_I2S_OUT_CON engine that
    serialises L/R samples towards the on-chip HDMI transmitter.

Sample-rate programming uses the empirically determined
HDMI_BCK_DIV = 45 * 48000 / rate - 1 formula in AUDIO_TOP_CON3,
which covers 44.1 kHz and 48 kHz within the 6-bit divider range.
The AFE_HDMI_CONN0 interconnect is programmed to route memif
output pairs to the serializer inputs with L/R in the right order
for hdmi-audio-codec.

The existing I2S engine helpers (mt2701_mclk_configuration,
mt2701_i2s_path_enable, mt2701_afe_i2s_path_disable) are reused
for the HDMI BE so that MCLK at 128*fs and the ASYS I2S3 FS field
are programmed and cleanly released across open/close cycles.

Only S16_LE and 44.1k/48k are exposed to userspace. Other rates
fall outside the 6-bit BCK divider range, and wider sample
formats require DMA BIT_WIDTH programming that the current memif
setup does not handle. These limits match what the MT8173 AFE
driver exposes for its HDMI path.

The HDMI-related AFE registers (AUDIO_TOP_CON3, AFE_HDMI_OUT_CON0,
AFE_HDMI_CONN0, AFE_8CH_I2S_OUT_CON) are added to the suspend
backup list so that the existing mtk_afe_suspend/resume framework
saves and restores them across system sleep cycles.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://patch.msgid.link/a580d6d676bcdba3d8bad94bb3bcb91a336bf1ba.1776998727.git.daniel@makrotopia.org
Signed-off-by: Mark Brown <broonie@kernel.org>