KVM: arm64: Rename __pkvm_pgtable_stage2_unmap()

KVM: arm64: Rename __pkvm_pgtable_stage2_unmap()

In preparation for adding support for protected VMs, where pages are
donated rather than shared, rename __pkvm_pgtable_stage2_unmap() to
__pkvm_pgtable_stage2_unshare() to make it clearer about what is going
on.

Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Tested-by: Mostafa Saleh <smostafa@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://patch.msgid.link/20260330144841.26181-5-will@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>