Currently, the kernel can write to 0xb80000 because this is part of the
initial identify mapping set up by the rt0 code. When we establish new
mappings for the kernel using its real VMA address then writes to the
framebuffer will cause a page fault unless we explicitly map it.
This commit removes the HWProbes() function from the console and tty
packages and replaces it with a global ProbeFuncs slice which is fetched
by the hal package when the hardware autodetection code runs.
Each driver should provide an init() function that appends a probe function
to the global ProbeFuncs slice.
This approach allows us to support conditional compilation of drivers in
the future (e.g. using build tags)
