This change is another minor step towards removing `AK::String` from
the Kernel. Instead of dynamically allocating the storage_name we can
instead allocate it via a KString in the factory for each device, and
then push the device name down into the StorageDevice base class.
We don't have a way of doing `AK::String::formatted(..)` with a KString
at the moment, so cleaning that up will be left for a later day.
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