New generic branch prediction

[jj16791]

These developments implement a new GenericPredictor class which contains:

• Static predictor based on pre-allocated branch type.
• A Branch Target Buffer (BTB) with a local and global indexing scheme and a 2-bit saturating counter.
• A Return Address Stack (RAS) is also in use.

Various changes have occurred to the parent branch class including:

• The passing of a branch type to help prediction (i.e. always taking unconditional branches)
• The passing of a known target extracting during pre-decoding to help prediction (i.e branch instructions to labels)
• Callable flush logic for the associated branch prediction schemes with an address as the parameter

[FinnWilkinson]

LGTM