Kernel: Add typed_map<T>(PhysicalAddress) and use it in ACPI parsing

There was a frequently occurring pattern of "map this physical address
into kernel VM, then read from it, then unmap it again".

This new typed_map() encapsulates that logic by giving you back a
typed pointer to the kind of structure you're interested in accessing.

It returns a TypedMapping<T> that can be used mostly like a pointer.
When destroyed, the TypedMapping object will unmap the memory. :^)

Kernel/ACPI/Initialize.cpp

@@ -53,7 +53,7 @@ void initialize()
     if (feature_level == FeatureLevel::Disabled)
         return;
 
-    auto rsdp = StaticParsing::search_rsdp();
+    auto rsdp = StaticParsing::find_rsdp();
     if (rsdp.is_null())
         return;