selftests/vm: run_vmtests.sh: update and clean up gup_test invocation

selftests/vm: run_vmtests.sh: update and clean up gup_test invocation

Run benchmarks on the _fast variants of gup and pup, as originally
intended.

Run the new gup_test sub-test: dump pages.  In addition to exercising the
dump_page() call, it also demonstrates the various options you can use to
specify which pages to dump, and how.

Link: https://lkml.kernel.org/r/20201026064021.3545418-8-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>