target/arm: Avoid bare abort() or assert(0)

target/arm: Avoid bare abort() or assert(0)

Standardize on g_assert_not_reached() for "should not happen".
Retain abort() when preceeded by fprintf or error_report.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20220501055028.646596-7-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>