kitty: move to using sDDF graphics protocol

[Ivan-Velickovic]

Right now the Kitty client has access to the GPU/display via an exported framebuffer from a Linux VM.

Presently, this is pretty much a hack even though it works.

We now have an initial (but immature) design for 2D graphics in the seL4 Device Driver Framework and so we should transition the Kitty example to use that protocol/interface instead.