dt-bindings: clock: mt7622: Add AFE_MRGIF clock

Add the missing AFE Merge Interface clock to MT7622 to make use of
it in the audio subsystem.

While at it, also remove the useless CLK_AUDIO_NR_CLK definition.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>