Add task creation and fix Task_yield procedure

kernel/aarch64/aarch64.S

@@ -122,6 +122,17 @@ AArch64_memzero:
 die:
 	b die
 
+.globl AArch64_startTask 
+AArch64_startTask:
+	bl Task_unlockScheduler
+	blr x1
+	
+hang:
+	/* todo: implement task exit here */
+	WFE
+	b hang
+
+
 .globl AArch64_switchContext
 AArch64_switchContext:
 	/* Save current task context */

kernel/aarch64/aarch64.h

@@ -43,6 +43,9 @@ AArch64_disableIRQ(void);
 extern void
 AArch64_memzero(void *addr, unsigned long size);
 
+extern void
+AArch64_startTask(void *arg, void *callback);
+
 extern void
 AArch64_switchContext(void *currentTask, void *nextTask);