[SRU T/U/V] Fix vesafb performance regression

[Stefan Bader]

BugLink: http://bugs.launchpad.net/bugs/1434581

In a release long long ago, we modified vesafb to be compilable as
a module. Starting with Oneiric the default mtrr setting was changed
(apparently on maintainers advice) to write-combining. This way we
probably still would boot merrily after if not for dropping the change
to make vesafb a module between Saucy and Trusty. By then the mtrr
change had been devoured by the module patch and so the framebuffer
mapping was no longer cached by default.

Assuming that O->S was long enough to declare this stable, the attached
patches re-introduce the new default. The only difference between the
Trusty variant and the other is that vesafb.c got relocated.

-Stefan