Large stack frame patch for the CellSPU: handle stack frames that exceed 8176

(511*16) bytes register displacement (D-form).

NOTE: This is a potential headache, given the SPU's local core limitations,
allowing the software developer to commit stack overrun suicide unknowingly.
Also, large SPU stack frames will cause code size explosion. But, one presumes
that the software developer knows what they're doing...

Contributed by Kalle.Raiskila@nokia.com, edited slightly before commit.

llvm-svn: 97091