hw/uefi: Create and use trace.h wrapper header

hw/uefi: Create and use trace.h wrapper header

The documentation of the trace subsystem (docs/devel/tracing.rst)
says that each subdirectory which uses trace events should create a
wrapper trace.h file which includes the trace/trace-foo.h generated
header, and that .c files then #include "trace.h".

We didn't follow this pattern in hw/uefi/.  Correct this by creating
and using the trace.h wrapper header.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>