Patch to (almost) completly update frv port to use target hooks

[Graham Stott]

Neil Booth wrote:
> Kaveh R. Ghazi wrote:-
> 

> Zack put them in one of the headers (system.h?) which should be included
> first.
I moved them from system.h to config.h which is always included first so
#ifdef TREE_CODE and #ifdef RTX_CODE are never needed to protect uses of
tree and rtx typedefs.

> 
> Neil.
> 

Graham