target/arm: Rename FPSR_MASK and FPCR_MASK and define them symbolically

target/arm: Rename FPSR_MASK and FPCR_MASK and define them symbolically

Now that we store FPSR and FPCR separately, the FPSR_MASK and
FPCR_MASK macros are slightly confusingly named and the comment
describing them is out of date.  Rename them to FPSCR_FPSR_MASK and
FPSCR_FPCR_MASK, document that they are the mask of which FPSCR bits
are architecturally mapped to which AArch64 register, and define them
symbolically rather than as hex values.  (This latter requires
defining some extra macros for bits which we haven't previously
defined.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20240628142347.1283015-9-peter.maydell@linaro.org