KVM: arm64: Drop pkvm_mem_transition for host/hyp sharing

Simplify the __pkvm_host_{un}share_hyp() paths by not using the
pkvm_mem_transition machinery. As there are the last users of the
do_share()/do_unshare(), remove all the now-unused code as well.

No functional changes intended.

Signed-off-by: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20250110121936.1559655-3-qperret@google.com


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