It's 90Kg for each tyre and it is total load i.e. the bike, you and your luggage. For example, let's say your bike's weight distribution is 50/50 (not likely but it makes for an easy calculation

), you weigh 70Kg, your bike is 10Kg and your luggage is 10Kg, total weight = 90Kg so according to the weight distribution you have a 45Kg load on each wheel, so well within the 90Kg max load of the tyre.