BitField: Add a static_assert.

Being able to store BitField within unions requires BitField to be of standard layout, which in turn is only given if the underlying type is also has standard layout.
BitField: Cast enum values to proper integer type.
GPU debugger: Don't keep track of debugging data if no debugger views are active.
Use a more compatible choice of initial framebuffer addresses.
GSP: Implement ReadHWRegs and WriteHWRegs properly.
GSP: HLE GXCommandId::SET_DISPLAY_TRANSFER and GXCommandId::SET_TEXTURE_COPY.
GPU: Add display transfer configuration. - e2d3d515a2ca0541174f68fa509539dfda3d055a

Squash in the commit before the last one.. - 9753b8a5d0ec63e19cd3e978909676093fb137da
GPU: Properly implement display transfers.
GPU: Add proper framebuffer register handling.
GPU: Emulate memory fills.
GPU: Initialize GPU registers to some sensible default state.
GPU: Interface cleanup.
Renderer: Add a few TODOs.
Renderer: Respect the active_fb GPU register.
Renderer: Fix component order in bottom framebuffer.
GPU: Make framebuffer code format-aware.
GPU: Make use of RegisterSet.
RegisterSet: Simplify code by using structs for register definition instead of unions.