Kernel: Implement __panic() for the aarch64 Kernel

Now that dump_backtrace() works, we can actually print a helpful
backtrace when the Kernel panics.

Kernel/CMakeLists.txt

@@ -418,6 +418,7 @@ else()
         Arch/aarch64/kprintf.cpp
         Arch/aarch64/MainIdRegister.cpp
         Arch/aarch64/PageDirectory.cpp
+        Arch/aarch64/Panic.cpp
         Arch/aarch64/SafeMem.cpp
         Arch/aarch64/ScopedCritical.cpp
         Arch/aarch64/SmapDisabler.cpp