Add bindings for common parts (platform) of Universal Flash Storage
(UFS) Host Controllers in dtschema format.

Include also the bindings directory in the UFS maintainers entry.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220306111125.116455-2-krzysztof.kozlowski@canonical.com