dt-bindings: mmc: sdhci-of-dwcmhsc: Add T-Head TH1520 support

Add compatible value for the T-Head TH1520 dwcmshc controller.

Acked-by: Guo Ren <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Drew Fustini <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml

···
       - rockchip,rk3568-dwcmshc
       - rockchip,rk3588-dwcmshc
       - snps,dwcmshc-sdhci
+      - thead,th1520-dwcmshc
 
   reg:
     maxItems: 1