Platform/ARM: add CXL driver

This patch introduces CXL Dxe, which primarily discovers a PCIe device
with CXL capability and configures the same.

This patch creates and registers event notifier based on
gEfiPciEnumerationCompleteProtocolGuid. Once PCIe enumeration is
completed then CXL Dxe triggers function to discover CXL capable device
with memory expander capability and reads out memory range details.

In addition to find out a PCIe device with CXL Mem extended capability,
the module also looks for CXL device with DOE capability. Once DOE
capability is found, then execute DOE operation to fetch CDAT
structures(DSMAS), which carry information about CXL Device Memory
range, type of memory etc. It stores the remote CXL memory details in
local data structure.

Later it installs CXL Protocol interface, which will trigger
AcpiTableGenerator module to fetch CXL memory details using CXL protocol
interfaces for preparation of ACPI tables.

Signed-off-by: Sayanta Pattanayak <sayanta.pattanayak@arm.com>
Change-Id: I612ed13b6a6bdb27d8ed4ced87f72a33dbbcc4b4