target/mips: fpu: Refactor conversion from ieee to mips exception flags

target/mips: fpu: Refactor conversion from ieee to mips exception flags

The original coversion function is used for regular and MSA floating
point instructions handling. Since there are some nuanced differences
between regular and MSA floating point exception handling, provide two
instances of the conversion function, rather than just a single common
one. Inline both instances of this function instances for the sake of
performance. Improve variable naming in surrounding code for clarity.

Reviewed-by: Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>
Signed-off-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Message-Id: <20200518200920.17344-17-aleksandar.qemu.devel@gmail.com>