drm/i915/dram: replace __raw_uncore_read32() with intel_uncore_read_fw()

The __raw_uncore_* interface is supposed to be intel_uncore.[ch]
internal only. Replace the remaining outside user with
intel_uncore_read_fw(), which is essentially the same thing.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230627105849.274263-1-jani.nikula@intel.com