Rename K0501W to include PCB version

It seems very likely that other versions are not compatible, so make it
clear by including it in the machine type and name. Also update the
documentation.

machine.c

@@ -409,9 +409,9 @@ void machine_custom_init(void) {
 	reg_bit_set(RTL837X_REG_LED_GLB_IO_EN, 6);
 }
 
-#elif defined MACHINE_K0501W
+#elif defined MACHINE_K0501W_V2_0
 __code const struct machine machine = {
-	.machine_name = "K0501W",
+	.machine_name = "K0501W V2.0",
 	.isRTL8373 = 0,
 	.min_port = 3,
 	.max_port = 8,