target/arm/hvf: Add trace.h header

target/arm/hvf: Add trace.h header

The documentation for trace events says that every subdirectory which
has trace events should have a trace.h header, whose only content is
an include of the trace/trace-<subdir>.h file.

When we added the trace events in target/arm/hvf/ we forgot to create
this file and instead hvf.c directly includes
trace/trace-target_arm_hvf.h.

Create the standard trace.h file to bring this into line with the
convention.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20241108162909.4080314-3-peter.maydell@linaro.org