In v8.1M, vector table fetch failures don't set HFSR.FORCED (see rule
R_LLRP).  (In previous versions of the architecture this was either
required or IMPDEF.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201119215617.29887-18-peter.maydell@linaro.org