x32: Provide separate is_ia32_task() and is_x32_task() predicates

The is_compat_task() test is composed of two predicates already, so
make each of them available separately.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: H. J. Lu <hjl.tools@gmail.com>
Link: http://lkml.kernel.org/r/1329696488-16970-1-git-send-email-hpa@zytor.com