docs: create Cache Allocation Technology (CAT) and Code and Data Prioritization ...

docs: create Cache Allocation Technology (CAT) and Code and Data Prioritization (CDP) feature document

This patch creates CAT and CDP feature document in doc/features/. It describes
key points to implement L3 CAT/CDP and L2 CAT which is described in details in
Intel SDM "INTEL® RESOURCE DIRECTOR TECHNOLOGY (INTEL® RDT) ALLOCATION FEATURES".

Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>