uti: Replace data types represented as arrays with C structures

Defining C structures for the following objects:
(1) Remote and local context
(2) Stack of system call arguments / return values

Change-Id: Iafbb6c795bd765e3c78c54a255d8a1e4d4536288

kernel/include/syscall.h

@@ -590,6 +590,15 @@ typedef struct uti_attr {
 	uint64_t flags; /* Representing location and behavior hints by bitmap */
 } uti_attr_t;
 
+struct uti_ctx {
+	union {
+		char ctx[4096];
+		struct {
+			int uti_refill_tid;
+		};
+	};
+}; 
+
 struct move_pages_smp_req {
 	unsigned long count;
 	const void **user_virt_addr;