ACPICA: Drop Linux-specific waking vector functions

Commit f06147f9 (ACPICA: Hardware: Enable firmware waking vector
for both 32-bit and 64-bit FACS) added three functions that aren't
present in upstream ACPICA, acpi_hw_set_firmware_waking_vectors(),
acpi_set_firmware_waking_vectors() and acpi_set_firmware_waking_vector64(),
to allow Linux to use the previously existing API for setting the
platform firmware waking vector.

However, that wasn't necessary, since the ACPI sleep support code
in Linux can be modified to use the upstream ACPICA's API easily
and the additional functions may be dropped which reduces the code
size and puts the kernel's ACPICA code more in line with the upstream.

Make the changes as per the above.  While at it, make the relevant
function desctiption comments reflect the upstream ACPICA's ones.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Lv Zheng <lv.zheng@intel.com>