target-arm: Drop CPUARMState* argument from bank_number()

Drop the CPUARMState* argument from bank_number(), since we only
use it for passing to cpu_abort(). Use hw_error() instead.
This avoids propagating further interfaces using env pointers.

In the long term this function's callers need auditing to fix
problems where badly behaved guests can pass invalid bank numbers.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andreas Färber <afaerber@suse.de>
