target/arm: LD1Q, ST1Q are vector + scalar, not scalar + vector

target/arm: LD1Q, ST1Q are vector + scalar, not scalar + vector

Unlike the "LD1D (scalar + vector)" etc instructions, LD1Q is
vector + scalar. This means that:
 * the vector and the scalar register are in opposite fields
   in the encoding
 * 31 in the scalar register field is XZR, not XSP

The same applies for ST1Q.

This means we can't reuse the trans_LD1_zprz() and trans_ST1_zprz()
functions for LD1Q and ST1Q. Split them out to use their own
trans functions.

Note that the change made here to sve.decode requires the decodetree
bugfix "decodetree: Infer argument set before inferring format" to
avoid a spurious compile-time error about "dtype".

Fixes: d2aa9a804ee678f ("target/arm: Implement LD1Q, ST1Q for SVE2p1")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250723165458.3509150-5-peter.maydell@linaro.org