x86: Merge kernel_math_error() into math_error()

Clean up the kernel exception handling and make it more similar to
the other traps.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
LKML-Reference: <1269176446-2489-4-git-send-email-brgerst@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>