Hello,

This patch adds a per-architecture gdbarch_unwind_sp and the frame 
wrapper methods:
	get_frame_sp()
and
	frame_sp_unwind()
as replacements for TARGET_READ_SP.  The key advantage of this new 
method is that it takes a ``struct frame_info'' parameter and hence 
avoids any global state.

It also modifies read_sp() so that it will use get_frame_sp and hence 
provide a certain level of forward compatibility.  Similarly, 
frame_sp_unwind() has been written in a way that provides a certain 
level of backward compatibility.

For the d10v, sets UNWIND_SP instead of READ_SP and eliminates another 
global regcache/target reference.

Follow-on changes will include things like replace read_sp() with 
get_frame_sp(), eliminate generic_target_read_sp(), and deprecate 
TARGET_READ_SP.

Eli, note the doco change.

I'll look to commit this in a few days.

Andrew