KVM: arm64: nv: Introduce guest stage-2 tracking structures

In order to avoid unmapping all shadow stage-2 mappings when KVM
receives a MMU notifier unmap call, we have to keep track of the
canonical IPA -> nested IPA relationship of the shadow mappings
created. This essentially means tracking the guest's stage-2.

To do this, represent each mapping by struct kvm_guest_s2_mapping. It
stores the mapping's canonical IPA range and the nested IPA range using
two interval tree nodes. Both nodes will be inserted into their
respective interval trees called guest_s2_mappings. The canonical IPA
ranges will be stored in the tree within the canonical MMU, and the
nested IPA ranges will be stored in the corresponding nested MMU's tree.

For example:

struct kvm_guest_s2_mapping mapping1, mapping2;

    ---------------------> mapping2.canonical
    |                      mapping1.canonical
    |                          ^   (both stored in canonical mmu's tree)
    |                          |
--*****-----------------------*****----------- CIPA
   \\\\\                      |||||                  mapping1.nested_mmu
    \\\\\                     \\\\\                            |
     \\\\\                     \\\\\                           v
------\\\\\---------------------*****--------- NIPA #1 (nested mmu #1)
       \\\\\                      |
        \\\\\                     -> mapping1.nested
         \\\\\                       (stored in nested mmu #1's tree)
          \\\\\
-----------*****------------------------------ NIPA #2 (nested mmu #2)
             |                                                 ^
             -> mapping2.nested                                |
                (stored in nested mmu #2's tree)   mapping2.nested_mmu

Using the trees we can look up nodes in either of the IPA spaces, and
for each node, find the corresponding range in the other IPA space from
the other node in the enclosing kvm_guest_s2_mapping.

Define kvm_guest_s2_mapping and the interval tree here. Guest stage-2
mapping tracking will come in subsequent patches.

Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
Reviewed-by: Oliver Upton <oupton@kernel.org>
Tested-by: Shuai Xue <xueshuai@linux.alibaba.com>
Tested-by: Itaru Kitayama <itaru.kitayama@fujitsu.com>
Link: https://patch.msgid.link/20260915154305.3852871-3-weilin.chang@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

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