target/arm: Rename sve_zcr_len_for_el to sve_vqm1_for_el

target/arm: Rename sve_zcr_len_for_el to sve_vqm1_for_el

This will be used for both Normal and Streaming SVE, and the value
does not necessarily come from ZCR_ELx.  While we're at it, emphasize
the units in which the value is returned.

Patch produced by
    git grep -l sve_zcr_len_for_el | \
    xargs -n1 sed -i 's/sve_zcr_len_for_el/sve_vqm1_for_el/g'

and then adding a function comment.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220607203306.657998-13-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>