target-arm: Implement handling of breakpoint firing

Implement handling of breakpoint event firing to correctly
inject the debug exception into the guest.

Since the breakpoint and watchpoint control register format is
very similar we adjust wp_matches() to also handle breakpoints
as well rather than using a separate function.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1410523465-13400-3-git-send-email-peter.maydell@linaro.org