ARM64 / ACPI: If we chose to boot from acpi then disable FDT

If the early boot methods of acpi are happy that we have valid ACPI
tables and acpi=force has been passed, then do not unflat devicetree
effectively disabling further hardware probing from DT.

CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Will Deacon <will.deacon@arm.com>
Tested-by: NSuravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Tested-by: NYijing Wang <wangyijing@huawei.com>
Tested-by: NMark Langsdorf <mlangsdo@redhat.com>
Tested-by: NJon Masters <jcm@redhat.com>
Tested-by: NTimur Tabi <timur@codeaurora.org>
Tested-by: NRobert Richter <rrichter@cavium.com>
Acked-by: NRobert Richter <rrichter@cavium.com>
Acked-by: NOlof Johansson <olof@lixom.net>
Acked-by: NGrant Likely <grant.likely@linaro.org>
Signed-off-by: NGraeme Gregory <graeme.gregory@linaro.org>
Signed-off-by: NHanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/kernel/setup.c

@@ -390,7 +390,8 @@ void __init setup_arch(char **cmdline_p)
 
 	early_ioremap_reset();
 
-	unflatten_device_tree();
+	if (acpi_disabled)
+		unflatten_device_tree();
 
 	psci_init();