selftests/vm: enable running select groups of tests

Our memory management kernel CI testing at Red Hat uses the VM
selftests and we have run into two problems:

First, our LTP tests overlap with the VM selftests.

We want to avoid unhelpful redundancy in our testing practices.

Second, we have observed the current run_vmtests.sh to report overall
failure/ambiguous results in the case that a machine lacks the necessary
hardware to perform one or more of the tests. E.g. ksm tests that
require more than one numa node.

We want to be able to run the vm selftests suitable to particular hardware.

Add the ability to run one or more groups of vm tests via run_vmtests.sh
instead of simply all-or-none in order to solve these problems.

Preserve existing default behavior of running all tests when the script
is invoked with no arguments.

Documentation of test groups is included in the patch as follows:

    # ./run_vmtests.sh [ -h || --help ]

    usage: ./tools/testing/selftests/vm/run_vmtests.sh [ -h | -t "<categories>"]
      -t: specify specific categories to tests to run
      -h: display this message

    The default behavior is to run all tests.

    Alternatively, specific groups tests can be run by passing a string
    to the -t argument containing one or more of the following categories
    separated by spaces:
    - mmap
	    tests for mmap(2)
    - gup_test
	    tests for gup using gup_test interface
    - userfaultfd
	    tests for  userfaultfd(2)
    - compaction
	    a test for the patch "Allow compaction of unevictable pages"
    - mlock
	    tests for mlock(2)
    - mremap
	    tests for mremap(2)
    - hugevm
	    tests for very large virtual address space
    - vmalloc
	    vmalloc smoke tests
    - hmm
	    hmm smoke tests
    - madv_populate
	    test memadvise(2) MADV_POPULATE_{READ,WRITE} options
    - memfd_secret
	    test memfd_secret(2)
    - process_mrelease
	    test process_mrelease(2)
    - ksm
	    ksm tests that do not require >=2 NUMA nodes
    - ksm_numa
	    ksm tests that require >=2 NUMA nodes
    - pkey
	    memory protection key tests
    - soft_dirty
    	    test soft dirty page bit semantics
    - anon_cow
            test anonymous copy-on-write semantics
    example: ./run_vmtests.sh -t "hmm mmap ksm"

Link: https://lkml.kernel.org/r/20221018231222.1884715-1-jsavitz@redhat.com


Signed-off-by: Joel Savitz <jsavitz@redhat.com>
Cc: Joel Savitz <jsavitz@redhat.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>