[PATCH] powerpc: move rtas_fw.c out of platforms/pseries

Cell uses the same code as pSeries for flashing the firmware
through rtas, so the implementation should not be part of
platforms/pseries.

Put it into arch/powerpc/kernel instead.

Signed-off-by: Arnd Bergmann <arndb@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>