UPSTREAM: Docs: KVM: Rename psci.rst to hypercalls.rst

Since the doc also covers general hypercalls' details,
rather than just PSCI, and the fact that the bitmap firmware
registers' details will be added to this doc, rename the file
to a more appropriate name- hypercalls.rst.

Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220502233853.1233742-6-rananta@google.com


(cherry picked from commit f1ced23a)
Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 233587962
Bug: 233588291
Change-Id: I806913743b0ed2150eef9933c2961ea97b28ebfb