Add compatible strings for sm8150 and sm8250 iommus to documentation.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200609194030.17756-2-jonathan@marek.ca


Signed-off-by: Will Deacon <will@kernel.org>