KVM: arm64: Drop pkvm_mem_transition for FF-A

Simplify the __pkvm_host_{un}share_ffa() paths by using
{check,set}_page_state_range().

No functional changes intended.

Signed-off-by: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20250110121936.1559655-2-qperret@google.com


Signed-off-by: Marc Zyngier <maz@kernel.org>