ASoC: mediatek: mt8173-rt5650: Rename Speaker control to Ext Spk

Some RT5645 and RT5650 powered platforms are using "Ext Spk"
instead of "Speaker", and this is also reflected in alsa-lib
configurations for the generic RT5645 usecase manager configs.

Rename the "Speaker" control to "Ext Spk" in order to be able
to make the userspace reuse/inherit the same configurations also
for this machine, along with the others.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20211105152013.75252-1-angelogioacchino.delregno@collabora.com
Signed-off-by: Mark Brown <broonie@kernel.org>