libperf tests: Add support for verbose printing

Add __T_VERBOSE() so tests can add verbose output. The verbose output is
enabled with the '-v' command line option. Running 'make tests V=1' will
enable the '-v' option when running the tests.

It'll be used in the next patch, for a user space counter access test.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Itaru Kitayama <itaru.kitayama@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Link: http://lore.kernel.org/lkml/20210414155412.3697605-3-robh@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>