target/i386: Check for USER_ONLY definition instead of SOFTMMU one

Since we *might* have user emulation with softmmu,
replace the system emulation check by !user emulation one.

(target/ was cleaned from invalid CONFIG_SOFTMMU uses at
commit cab35c73, but these files were merged few days
after, thus missed the cleanup.)

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231004082239.27251-1-philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>