Start split out of common open firmware code

This creates drivers/of/base.c (depending on CONFIG_OF) and puts
the first trivially common bits from the prom.c files into it.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Paul Mackerras <paulus@samba.org>
Acked-by: David S. Miller <davem@davemloft.net>
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 603d83a..9d327ec 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -24,6 +24,9 @@
 config ARCH_NO_VIRT_TO_BUS
 	def_bool y
 
+config OF
+	def_bool y
+
 source "init/Kconfig"
 
 menu "General machine setup"