ANDROID: mthp: Fixup ABI for frag list

Introduce swap_info_ext struct

Move the added frag_clusters and frag_cluster_nr fields
out of swap_info_struct and into the swap_info_ext struct;
to maintain ABI compatibilty.

The swap type is used the get the corresponding swap_info_ext
for a give swap_info_struct.

Ensure that swap_info_ext is allocated and freed
along with swap_info_struct.

Change-Id: If4bcc8a1828dc65048dc2681a70cefcba6968c66
Bug: 313807618
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>