ARM64 / ACPI: Don't unflatten device tree if acpi=force is passed

Since the policy is that once we pass acpi=force in the early
param, we will not unflatten device tree even if ACPI is disabled
in ACPI table init fails, so fix the code by comparinging both
acpi_disabled and param_acpi_force before the device tree is
unflattened.

CC: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>