ANDROID: KVM: arm64: Flush cache on pKVM heap reclaim

The host is free to reclaim unused pages from the pKVM hyp heap
allocator. Before giving back this memory to this host, it is zeroed,
but this is not enough to ensure that will never be read. A non-cacheble
mapping in the host could still access the non-erased memory. Fix this
hole by flushing the cache after zero.

Bug: 340242767
Bug: 273748186
Bug: 2787496
Change-Id: Ic4d6b91683738c67bbb2acfabcaa23c38b48136a
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>