ACPI: use LNXCPU, not ACPI_CPU, for Linux-specific processor _HID

ACPI: use LNXCPU, not ACPI_CPU, for Linux-specific processor _HID

ACPI_PROCESSOR_OBJECT_HID is a synthetic _HID that Linux generates
for "Processor" definitions.  Unlike "Device" definitions, "Processor"
definitions do not have a _HID in the namespace, so we generate a
fake _HID.  By convention, all these fake _HIDs begin with "LNX".

This does change the user-visible _HID for "Processor" objects --
previously, we used "ACPI_CPU" and this changes that to "LNXCPU",
which starts with "LNX" as do all the other made-up _HIDs.  This
change is visible in processor filenames and "hid" files under
/sys/devices/LNXSYSTM:00/.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>