Increase kernel stack size to 2mb, move from cooperative to timer

preemption based scheduling, add correct save_lock on aarch64, add
simple IPC (read, write, manage), and simple and unsecure SHM, add
per-process kernel stacks, add copy_cstr_to_user, always use run_next
for aarch64, remove primitives from the kernel

kernel/src/config.rs

@@ -1,2 +1,2 @@
 pub const TIMER_FREQUENCY_HZ: usize = 1000;
-pub const KARCH: &str = "x86_64";
+pub const KARCH: &str = "aarch64";