KVM: arm64: Combine visitor arguments into a context structure

Passing new arguments by value to the visitor callbacks is extremely
inflexible for stuffing new parameters used by only some of the
visitors. Use a context structure instead and pass the pointer through
to the visitor callback.

While at it, redefine the 'flags' parameter to the visitor to contain
the bit indicating the phase of the walk. Pass the entire set of flags
through the context structure such that the walker can communicate
additional state to the visitor callback.

No functional change intended.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Ben Gardon <bgardon@google.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221107215644.1895162-2-oliver.upton@linux.dev