Improve the exception-taken logging by logging in
v7m_exception_taken() the exception we're going to take
and whether it is secure/nonsecure.

This requires us to move logging at many callsites from after the
call to before it, so that the logging appears in a sensible order.

(This will make tail-chaining produce more useful logs; for the
current callers of v7m_exception_taken() we know which exception
we're going to take, so custom log messages at the callsite sufficed;
for tail-chaining only v7m_exception_taken() knows the exception
number that we're going to tail-chain to.)
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180720145647.8810-2-peter.maydell@linaro.org