bus: tegra-gmi: Replace of_platform.h with explicit includes

Tegra-gmi doesn't use anything from of_platform.h, but depends on
of.h, of_device.h, and platform_device.h which are all implicitly
included, but that is going to be removed soon.

Link: https://lore.kernel.org/r/20230410232735.1562296-1-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>