ANDROID: KVM: arm64: Allow post-freeze backports to pKVM

The GKI policy allows the addition of new symbols to a frozen KMI as
long as doing so has no impact on existing frozen symbols. Interestingly
the hypervisor's ABI is defined by the pkvm_module_ops structure. Any
addition to this struct will be flagged as a type change, which equates
to a KMI breakage in the GKI world. This could become a major problem
long term if it prevented backport of (security) fixes to KMI-frozen
kernels.

To allow such backports, add a set of reserved ABI slots to the
pkvm_module_ops struct. These slots are usually reserved to fix LTS
merges, but given that none of the pKVM module code is upstream yet,
these slots are likely to be used by Android-specific fixes.

Bug: 278749606
Bug: 233587962
Change-Id: I61a00a09947ccff153c96a4829e083ef9ede19d3
Signed-off-by: Quentin Perret <qperret@google.com>