accel: Introduce current_accel_name()

accel: Introduce current_accel_name()

We need to fetch the name of the current accelerator in flexible error
messages more going forward. Let's create a helper that gives it to us
without casting in the target code.

Signed-off-by: Alexander Graf <agraf@csgraf.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220620192242.70573-1-agraf@csgraf.de
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>