KVM: arm64: Rename firmware pseudo-register documentation file

In preparation for describing the guest view of KVM/arm64 hypercalls in
hypercalls.rst, move the existing contents of the file concerning the
firmware pseudo-registers elsewhere.

Cc: Raghavendra Rao Ananta <[e-mail]>
Signed-off-by: Will Deacon <[e-mail]>
Signed-off-by: Fuad Tabba <[e-mail]>
Acked-by: Oliver Upton <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Marc Zyngier <[e-mail]>

Documentation/virt/kvm/arm/hypercalls.rst Documentation/virt/kvm/arm/fw-pseudo-registers.rst

···
 .. SPDX-License-Identifier: GPL-2.0
 
-=======================
-ARM Hypercall Interface
-=======================
+=======================================
+ARM firmware pseudo-registers interface
+=======================================
 
 KVM handles the hypercall services as requested by the guests. New hypercall
 services are regularly made available by the ARM specification or by KVM (as

Documentation/virt/kvm/arm/index.rst

···
 .. toctree::
    :maxdepth: 2
 
+   fw-pseudo-registers
    hyp-abi
-   hypercalls
    pvtime
    ptp_kvm
    vcpu-features