KVM: arm64: Document the KVM/arm64-specific calls in hypercalls.rst

KVM/arm64 makes use of the SMCCC "Vendor Specific Hypervisor Service
Call Range" to expose KVM-specific hypercalls to guests in a
discoverable and extensible fashion.

Document the existence of this interface and the discovery hypercall.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Fuad Tabba <tabba@google.com>
Acked-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240423150538.2103045-28-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

Docs: KVM: Add doc for the bitmap firmware registers

Add the documentation for the bitmap firmware registers in
hypercalls.rst and api.rst. This includes the details for
KVM_REG_ARM_STD_BMAP, KVM_REG_ARM_STD_HYP_BMAP, and
KVM_REG_ARM_VENDOR_HYP_BMAP registers.

Since the document is growing to carry other hypercall related
information, make necessary adjustments to present the document
in a generic sense, rather than being PSCI focused.

Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
[maz: small scale reformat, move things about, random typo fixes]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220502233853.1233742-7-rananta@google.com

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