Commit a2b0a27d ("target/mips: Move TCG source files under
tcg/ sub directory") forgot to move the trace-event file.
As it only contains TCG events, move it for consistency.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210617174323.2900831-4-f4bug@amsat.org>