[zion] Dynamically check Capability type.

Instead of passing an enum with the capability when creating it, relying
on polymorphism and a template struct tag to determine the object type
at runtime.

This is cleaner and avoids errors where we pass the wrong capability
type with the cap and do a bad cast at runtime.

zion/CMakeLists.txt

@@ -1,7 +1,6 @@
 add_executable(zion
   boot/acpi.cpp
   boot/boot_info.cpp
-  capability/capability.cpp
   capability/capability_table.cpp
   common/gdt.cpp
   common/load_gdt.s