Implement genAsm on aarch64

Add remaining PCS info: param and return registers in procedure calls.

src/codegen/aarch64.zig

@@ -59,6 +59,8 @@ pub const callee_preserved_regs = [_]Register{
     .x19, .x20, .x21, .x22, .x23,
     .x24, .x25, .x26, .x27, .x28,
 };
+pub const c_abi_int_param_regs = [_]Register{ .x0, .x1, .x2, .x3, .x4, .x5, .x6, .x7 };
+pub const c_abi_int_return_regs = [_]Register{ .x0, .x1 };
 
 test "Register.id" {
     testing.expectEqual(@as(u5, 0), Register.x0.id());
@@ -215,7 +217,7 @@ pub const Instruction = union(enum) {
 
     // Supervisor Call
 
-    fn svc(imm16: u16) Instruction {
+    pub fn svc(imm16: u16) Instruction {
         return supervisorCall(imm16);
     }
 };