KVM: arm64: Update MAINTAINERS to include selftests

As the KVM/arm64 selftests are routed via the kvmarm tree,
add the relevant references to the MAINTAINERS file.
Suggested-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210622070732.zod7gaqhqo344vg6@gator

MAINTAINERS

@@ -9993,6 +9993,8 @@ F:	arch/arm64/include/asm/kvm*
 F:	arch/arm64/include/uapi/asm/kvm*
 F:	arch/arm64/kvm/
 F:	include/kvm/arm_*
+F:	tools/testing/selftests/kvm/*/aarch64/
+F:	tools/testing/selftests/kvm/aarch64/
 
 KERNEL VIRTUAL MACHINE FOR MIPS (KVM/mips)
 M:	Huacai Chen <chenhuacai@kernel.org>