PCI/ACPI: Prefer CXL _OSC instead of PCIe _OSC for CXL host bridges

OB In preparation for negotiating OS control of CXL _OSC features, do the
minimal enabling to use CXL _OSC to handle the base PCIe feature
negotiation. Recall that CXL _OSC is a super-set of PCIe _OSC and the
CXL 2.0 specification mandates: "If a CXL Host Bridge device exposes CXL
_OSC, CXL aware OSPM shall evaluate CXL _OSC and not evaluate PCIe
_OSC."

Rather than pass a boolean flag alongside @root to all the helper
functions that need to consider PCIe specifics, add is_pcie() and
is_cxl() helper functions to check the flavor of @root. This also
allows for dynamic fallback to PCIe _OSC in cases where an attempt to
use CXL _OXC fails. This can happen on CXL 1.1 platforms that publish
ACPI0016 devices to indicate CXL host bridges, but do not publish the
optional CXL _OSC method. CXL _OSC is mandatory for CXL 2.0 hosts.

Cc: Bjorn Helgaas <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Robert Moore <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Reviewed-by: Rafael J. Wysocki <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Vishal Verma <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dan Williams <[email protected]>

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