perf mem: Factor out a function to generate sort order

perf mem: Factor out a function to generate sort order

Now, "--phys-data" is the only option which impacts the sort order.  A
simple "if else" is enough to handle the option. But there will be more
options added, e.g. "--data-page-size", which also impact the sort
order. The code will become too complex to be maintained.

Divide the sort order string into several small pieces.  The first piece
is always the default sort string for LOAD/STORE.  Appends the specific
sort string if related option is applied.

No functional change.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Stephane Eranian <eranian@google.com>
Cc: Will Deacon <will@kernel.org>
Link: http://lore.kernel.org/lkml/20201216185805.9981-4-kan.liang@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>