KVM: arm64: nv: Select XARRAY_MULTI to fix build error

populate_nv_trap_config() uses xa_store_range(), which is only built
when XARRAY_MULTI is set, so select that symbol to prevent the build error.

aarch64-linux-ld: arch/arm64/kvm/emulate-nested.o: in function `populate_nv_trap_config':
emulate-nested.c:(.init.text+0x17c): undefined reference to `xa_store_range'

Fixes: e58ec47b ("KVM: arm64: nv: Add trap forwarding infrastructure")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: kvmarm@lists.linux.dev
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230816210949.17117-1-rdunlap@infradead.org