KVM: arm64: nv: Fix doc header layout for timers

Stephen reports that 'make htmldocs' spits out a warning
("Documentation/virt/kvm/devices/vcpu.rst:147: WARNING: Definition
list ends without a blank line; unexpected unindent.").

Fix it by keeping all the timer attributes on a single line.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Marc Zyngier <maz@kernel.org>