[PATCH] powerpc: move mmio_nvram.c over to arch/powerpc

The nvram code formally known as bpa_nvram.c is rather
generic really, so it is quite likely to be useful to
future boards not based on cell.

This patch puts it into arch/powerpc/sysdev.

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