ANDROID: mm: export unpack_shadow

The commit 56526cf9("ANDROID: mm: swap: export and whitelist
get_shadow_from_swap_cache") exports the api to get the shadow entry
from the swap cache which is then used to check if this entry can be
further pushed down to slower devices.

At present, we are manually extracting the information from this shadow
entry using the same macros being used by unpack_shadow(). Instead
export this function.

Bug: 369964379
Bug: 379616503
Change-Id: Id044add31434d234e4a6136f192c11ab20ad0985
Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>
(cherry picked from commit 1a3bbc19)