Use symbolic names for some MTRR bits instead of numbers in CAR code

Use symbolic names for some MTRR bits instead of numbers in CAR code

Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Acked-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@6493 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1