MIPS: Respect the FCSR exception mask for `si_code'

Respect the FCSR exception mask when interpreting the IEEE 754 exception
condition to report with SIGFPE in `si_code', so as not to use one that
has been masked where a different one set in parallel caused the FPE
hardware exception to trigger.  As per the IEEE Std 754 the Inexact
exception can happen together with Overflow or Underflow.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9703/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>