UPSTREAM: Documentation: KVM: Fix title level for PSCI_SUSPEND

The htmldoc build breaks in a funny way with:

<quote>
Sphinx parallel build error:
docutils.utils.SystemMessage: /home/sfr/next/next/Documentation/virt/kvm/api.rst:6175: (SEVERE/4) Title level inconsistent:

For arm/arm64:
^^^^^^^^^^^^^^
</quote>

Swap the ^^s for a bunch of --s...

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
[maz: commit message]
Signed-off-by: Marc Zyngier <maz@kernel.org>
(cherry picked from commit 582eb04e)
Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 233587962
Bug: 233588291
Change-Id: I86069da4db4439f36c38b0796e06f3789798b2f2