softmmu: Check watchpoints for read+write at once

softmmu: Check watchpoints for read+write at once

Atomic operations are read-modify-write, and we'd like to
be able to test both read and write with one call.  This is
easy enough, with BP_MEM_READ | BP_MEM_WRITE.

Add BP_HIT_SHIFT to make it easy to set BP_WATCHPOINT_HIT_*.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>