Since APD_ADDR(desc) is only used when CONFIG_X86_AMD_PLATFORM_DEVICE
or CONFIG_ARM64 is set, no need for the stub APD_ADDR(desc) definition
covering the other cases, so remove it.

Also update the comments for #endif.
Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>