ASoC: mt8183: add compatible string for using rt1015

Machines with rt1015 should use the compatible string
"mt8183-mt6358-ts3a227-rt1015".
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Link: https://lore.kernel.org/r/20200708113233.3994206-3-tzungbi@google.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/mt8183-mt6358-ts3a227-max98357.txt

-MT8183 with MT6358, TS3A227 and MAX98357 CODECS
+MT8183 with MT6358, TS3A227, MAX98357, and RT1015 CODECS
 
 Required properties:
-- compatible : "mediatek,mt8183_mt6358_ts3a227_max98357"
+- compatible : "mediatek,mt8183_mt6358_ts3a227_max98357" for MAX98357A codec
+               "mediatek,mt8183_mt6358_ts3a227_rt1015" for RT1015 codec
 - mediatek,platform: the phandle of MT8183 ASoC platform
 
 Optional properties: