target/arm: Use new FPCR_NZCV_MASK constant

target/arm: Use new FPCR_NZCV_MASK constant

We defined a constant name for the mask of NZCV bits in the FPCR/FPSCR
in the previous commit; use it in a couple of places in existing code,
where we're masking out everything except NZCV for the "load to Rt=15
sets CPSR.NZCV" special case.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201119215617.29887-12-peter.maydell@linaro.org