powerpc/32s: Remove m8260_gorom()

Last user of m8260_gorom() was removed by
Commit 917f0af9 ("powerpc: Remove arch/ppc and include/asm-ppc")
removed last user of m8260_gorom().

In fact m8260_gorom() was ported to arch/powerpc/ but the
platform using it died with arch/ppc/

Remove it.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/13f7532f21df3196e8c78b4f82a9c8d5487aca35.1620292185.git.christophe.leroy@csgroup.eu