target/arm: Implement store_cpu_field_low32() macro

target/arm: Implement store_cpu_field_low32() macro

We already have a load_cpu_field_low32() to load the low half of a
64-bit CPU struct field to a TCGv_i32; however we haven't yet needed
the store equivalent.  We'll want that in the next patch, so
implement it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20240628142347.1283015-6-peter.maydell@linaro.org