selftests/mm: skip thuge-gen test if system is not setup properly

selftests/mm: skip thuge-gen test if system is not setup properly

Make thuge-gen skip instead of fail when it can't run due to system
settings.  If shmmax is too small or no 1G huge pages are available, the
test now prints a warning and is marked as skipped.

-------------------
Before Patch:
-------------------
~ running ./thuge-gen
~ Bail out! Please do echo 262144 > /proc/sys/kernel/shmmax
~ Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
~ [FAIL]
not ok 28 thuge-gen ~ exit=1

-------------------
After Patch:
-------------------
~ running ./thuge-gen
~ ~ WARNING: shmmax is too small to run this test.
~ ~ Please run the following command to increase shmmax:
~ ~ echo 262144 > /proc/sys/kernel/shmmax
~ 1..0 ~ SKIP Test skipped due to insufficient shmmax value.
~ [SKIP]
ok 29 thuge-gen ~ SKIP

Link: https://lkml.kernel.org/r/20250816040113.760010-7-aboorvad@linux.ibm.com
Co-developed-by: Donet Tom <donettom@linux.ibm.com>
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>