Add a linked list allocator for heap that can now do 256 mib due to

frame allocator optimizations, make a basic init function in arch that
will initialize everything for a given arch. Add tests in kmain for
alloc, and add a Locked struct used for static mutables and the linked
list.

kernel/.cargo/config.toml

@@ -1,4 +1,4 @@
 [unstable]
     json-target-spec = true
     build-std-features = ["compiler-builtins-mem"]
-    build-std = ["core", "compiler_builtins"]
+    build-std = ["core", "compiler_builtins", "alloc"]