Simplify nand/nor/eqv and move their optimizations to and/or/xor
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6805 c046a42c-6fe2-441c-8c8c-71466251a162