selftests: mm: add KSM_MERGE_TIME tests

Add KSM_MERGE_TIME and KSM_MERGE_TIME_HUGE_PAGES tests with
size of 100.

./run_vmtests.sh -t ksm
-----------------------------
running ./ksm_tests -H -s 100
-----------------------------
Number of normal pages:    0
Number of huge pages:    50
Total size:    100 MiB
Total time:    0.399844662 s
Average speed:  250.097 MiB/s
[PASS]
-----------------------------
running ./ksm_tests -P -s 100
-----------------------------
Total size:    100 MiB
Total time:    0.451931496 s
Average speed:  221.272 MiB/s
[PASS]

Link: https://lkml.kernel.org/r/20230728164102.4655-1-ayush.jain3@amd.com


Signed-off-by: Ayush Jain <ayush.jain3@amd.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>