target/arm: Add sve-max-vq cpu property to -cpu max

target/arm: Add sve-max-vq cpu property to -cpu max

This allows the default (and maximum) vector length to be set
from the command-line.  Which is extraordinarily helpful in
debugging problems depending on vector length without having to
bake knowledge of PR_SET_SVE_VL into every guest binary.

Cc: [email protected] (3.0.1)
Signed-off-by: Richard Henderson <[email protected]>
Reviewed-by: Alex Bennée <[email protected]>
Tested-by: Alex Bennée <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>