perf build: Raise minimum shellcheck version to 0.7.2

Raise the minimum shellcheck version for perf builds to 0.7.2, so that
systems with shellcheck versions below 0.7.2 will automatically skip the
shell script checking, even if NO_SHELLCHECK is unset.

Since commit 241f21be7d0fdf3c ("perf test perftool_testsuite: Use
absolute paths"), shellcheck versions before 0.7.2 break the perf build
with several SC1090 [2] warnings due to its too strict dynamic source
handling [1], e.g.:

In tests/shell/base_probe/test_line_semantics.sh line 20:
. "$DIR_PATH/../common/init.sh"
^---------------------------^ SC1090: Can't follow non-constant source. Use a directive to specify location.

Fixes: 241f21be7d0fdf3c ("perf test perftool_testsuite: Use absolute paths")
Signed-off-by: Nicolas Schier <n.schier@avm.de>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jakub Brnak <jbrnak@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Nicolas Schier <nsc@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Philipp Hahn <p.hahn@avm.de>
Cc: Veronika Molnarova <vmolnaro@redhat.com>
Link: https://github.com/koalaman/shellcheck/issues/1998 # [1]
Link: https://www.shellcheck.net/wiki/SC1090
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>