KVM: arm64: Hook up donation hypercall to pkvm_pgtable_stage2_map()

KVM: arm64: Hook up donation hypercall to pkvm_pgtable_stage2_map()

Mapping pages into a protected guest requires the donation of memory
from the host.

Extend pkvm_pgtable_stage2_map() to issue a donate hypercall when the
target VM is protected. Since the hypercall only handles a single page,
the splitting logic used for the share path is not required.

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/20260330144841.26181-14-will@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>