ARM64: kernel: acpi: honour acpi=force command line parameter

If acpi=force is passed on the command line, it forces ACPI to be
the only available boot method, hence it must be left enabled even
if the initialization and sanity checks on ACPI tables fails.

This patch refactors ACPI initialization to prevent disabling ACPI
if acpi=force is passed on the command line.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>