stage2 sparcv9: Add list of preserved regs

src/arch/sparcv9/abi.zig

@@ -0,0 +1,9 @@
+const bits = @import("bits.zig");
+const Register = bits.Register;
+
+// Register windowing mechanism will take care of preserving registers
+// so no need to do it manually
+pub const callee_preserved_regs = [_]Register{};
+
+// pub const c_abi_int_param_regs = [_]Register{};
+// pub const c_abi_int_return_regs = [_]Register{};