Documentation/Changes: clean up mcelog paragraph

The paragraph on mcelog currently describes kernel v2.6.31. In that
kernel the mce code (for i386, that is) was in transition. Ever since
v2.6.32 the situation is much simpler (eg, mcelog is now needed to
process events on almost all x86 machines, i386 and x86-64). Since this
"document is designed to provide a list of the minimum levels of
software necessary to run the 3.0 kernels" let's just describe that
situation.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>