target/s390x: Use s390_skeys_get|set() helper

target/s390x: Use s390_skeys_get|set() helper

Commit c9274b6bf0 ("target/s390x: start moving TCG-only code
to tcg/") moved mem_helper.c, but the trace-events file is
still in the parent directory, so is the generated trace.h.

Call the s390_skeys_get|set() helper, removing the need
for the trace event shared with the tcg/ sub-directory,
fixing the following build failure:

 In file included from ../target/s390x/tcg/mem_helper.c:33:
 ../target/s390x/tcg/trace.h:1:10: fatal error: 'trace/trace-target_s390x_tcg.h' file not found
 #include "trace/trace-target_s390x_tcg.h"

Reported-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20240613104415.9643-3-philmd@linaro.org>