I haven't read the chapter about the ARM's LCD controller thoroughly, but at this time I'm guessing the display part itself must have some sort of controller which accepts the data to be displayed (character, icon) and activates the appropriate pixels. I mean, something with registers to store data and commands, and a certain amount of RAM for a characterset.
I'm thinking/guessing the display functions the same as a DOT matrix LCD for example, or isn't it? Is it something completely different?

Grtz, Arthur