sv: support remaining assignment operators

- Add support for: *=, /=, %=, <<=, >>=, <<<=, >>>=
- Unify existing support for: +=, -=, &=, |=, ^=

tests/simple/asgn_binop.sv

@@ -0,0 +1,23 @@
+`define TEST(name, asgnop)\
+	module test_``name ( \
+		input logic [3:0] a, b, \
+		output logic [3:0] c \
+	); \
+		always @* begin \
+			c = a; \
+			c asgnop b; \
+		end \
+	endmodule
+
+`TEST(add, +=)
+`TEST(sub, -=)
+`TEST(mul, *=)
+`TEST(div, /=)
+`TEST(mod, %=)
+`TEST(bit_and, &=)
+`TEST(bit_or , |=)
+`TEST(bit_xor, ^=)
+`TEST(shl, <<=)
+`TEST(shr, >>=)
+`TEST(sshl, <<<=)
+`TEST(sshr, >>>=)