target/arm: Introduce PREDDESC field definitions

target/arm: Introduce PREDDESC field definitions

Git-commit: b64ee454a4a086ed459bcda4c0bbb54e197841e4

SVE predicate operations cannot use the "usual" simd_desc
encoding, because the lengths are not a multiple of 8.
But we were abusing the SIMD_* fields to store values anyway.
This abuse broke when SIMD_OPRSZ_BITS was modified in e2e7168a214.

Introduce a new set of field definitions for exclusive use
of predicates, so that it is obvious what kind of predicate
we are manipulating.  To be used in future patches.

Cc: qemu-stable@nongnu.org
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210113062650.593824-2-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Bruce Rogers <brogers@suse.com>