target-sh4: check FD bit for FP instructions

Based on a patch from Vladimir Prus <vladimir@codesourcery.com>

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5970 c046a42c-6fe2-441c-8c8c-71466251a162
