KVM: arm64: Handle FFA_MEM_LEND calls from the host

Handle FFA_MEM_LEND calls from the host by treating them identically to
FFA_MEM_SHARE calls for the purposes of the host stage-2 page-table, but
forwarding on the original request to EL3.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>