MIPS: KVM: Wire up FPU capability

Now that the code is in place for KVM to support FPU in MIPS KVM guests,
wire up the new KVM_CAP_MIPS_FPU capability.

For backwards compatibility, the capability must be explicitly enabled
in order to detect or make use of the FPU from the guest.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Cc: linux-api@vger.kernel.org
Cc: linux-doc@vger.kernel.org

Documentation/virtual/kvm/api.txt

@@ -3312,6 +3312,19 @@ Parameters: none
 This capability enables the in-kernel irqchip for s390. Please refer to
 "4.24 KVM_CREATE_IRQCHIP" for details.
 
+6.9 KVM_CAP_MIPS_FPU
+
+Architectures: mips
+Target: vcpu
+Parameters: args[0] is reserved for future use (should be 0).
+
+This capability allows the use of the host Floating Point Unit by the guest. It
+allows the Config1.FP bit to be set to enable the FPU in the guest. Once this is
+done the KVM_REG_MIPS_FPR_* and KVM_REG_MIPS_FCR_* registers can be accessed
+(depending on the current guest FPU register mode), and the Status.FR,
+Config5.FRE bits are accessible via the KVM API and also from the guest,
+depending on them being supported by the FPU.
+
 7. Capabilities that can be enabled on VMs
 ------------------------------------------