target-i386: Remove redundant HF_SOFTMMU_MASK

'HF_SOFTMMU_MASK' is only set when 'CONFIG_SOFTMMU' is defined. So
there's no need in this flag: test 'CONFIG_SOFTMMU' instead.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20160715175852.30749-6-sergey.fedorov@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>