Documentation: Fix index.rst after psci.rst renaming

Fix the TOC in index.rst after psci.rst has been renamed to
hypercalls.rst.

Signed-off-by: Marc Zyngier <[e-mail]>
Reported-by: Stephen Rothwell <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/virt/kvm/arm/index.rst

···
    :maxdepth: 2
 
    hyp-abi
-   psci
+   hypercalls
    pvtime
    ptp_kvm