target/arm: HVC at EL3 should go to EL3, not EL2

AArch64 permits code at EL3 to use the HVC instruction; however the
exception we take should go to EL3, not down to EL2 (see the pseudocode
AArch64.CallHypervisor()). Fix the target EL.

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar@zeroasic.com>
Message-id: 20231109151917.1925107-1-peter.maydell@linaro.org