ANDROID: KVM: arm64: Cleanup unused ppage->pins

Since 10a77358 ("ANDROID: KVM: arm64: Allow relinqush for p-guest
with huge-mappings"), pKVM issues a hyp_req to ask for a huge-mapping
split before a page relinquish happens. This made the ppage->pins field
deprecated. This field was meant to handle the previous broken approach
of relinquish where the kvm_pinned_page tree wasn't updated on a block
split.

While at it, remove the now unnecessary error handling in
pkvm_call_hyp_nvhe_ppage(). The hypervisor can only split blocks behind
the back of the host in the guest_share_host case.

Bug: 439812370
Bug: 357781595
Bug: 278011447
Change-Id: I705a010be8afaaadc9ba15a2b2c02eb1efa2194c
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>