selftests/mm: vm_util: split up /proc/self/smaps parsing

selftests/mm: vm_util: split up /proc/self/smaps parsing

Upcoming changes want to reuse the /proc/self/smaps parsing logic to parse
the VmFlags field.

As that works differently from the currently parsed HugePage counters,
split up the logic so common functionality can be shared.

While reworking this code, also use the correct sscanf placeholder for the
"uint64_t thp" variable.

Link: https://lkml.kernel.org/r/20250114-virtual_address_range-tests-v4-3-6fd7269934a5@linutronix.de
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: kernel test robot <oliver.sang@intel.com>
Cc: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>