IOS HLE: Replace is_hardware with a proper device type

is_hardware is an obscure name (what does hardware mean?) and it forces
us to assume that anything that !is_hardware is a FileIO device. This
assumption prevents properly restoring OH0 child devices (which will be
implemented in the USB PR), so this commit replaces the is_hardware
bool with a device type.

Source/Core/Core/State.cpp

@@ -71,7 +71,7 @@ static Common::Event g_compressAndDumpStateSyncEvent;
 static std::thread g_save_thread;
 
 // Don't forget to increase this after doing changes on the savestate system
-static const u32 STATE_VERSION = 67;  // Last changed in PR 4634
+static const u32 STATE_VERSION = 68;  // Last changed in PR 4638
 
 // Maps savestate versions to Dolphin versions.
 // Versions after 42 don't need to be added to this list,