powerpc: Use TEXT_TEXT macro in linker script.

Rather than adding .ref.text to the powerpc linker script so that we
can use __REF on the powerpc architecture, it seems simpler to switch
to using the generic TEXT_TEXT macro.

Signed-off-by: Tim Abbott <tabbott@mit.edu>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>