Modularize interrupt handlers, split up scheduler and PIT interrupt handlers

kernel/kmain.c

@@ -45,9 +45,9 @@ void kmain(void) {
   log_bootinfo();
   log_time();
   gdt_init();
-  intr_init();
   pmm_init();
   vmm_init();
+  intr_init();
   randcrypto_init();
   ipc_mbusinit();
   dev_init();