target/i386: Wire up MXCSR.DE and FPUS.DE correctly

target/i386: Wire up MXCSR.DE and FPUS.DE correctly

The x86 DE bit in the FPU and MXCSR status is supposed to be set
when an input denormal is consumed. We didn't previously report
this from softfloat, so the x86 code either simply didn't set
the DE bit or else incorrectly wired it up to denormal_flushed,
depending on which register you looked at.

Now we have input_denormal_used we can wire up these DE bits
with the semantics they are supposed to have.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Link: https://lore.kernel.org/r/20250519145114.2786534-4-peter.maydell@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>