When switching to the DXE phase stack, set the frame pointer to zero so
that code walking the stack frame will not try to access stack frames
belonging to the old stack.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>