powerpc: Replace nvram_* extern declarations with standard header

Remove the nvram_read_byte() and nvram_write_byte() declarations in
powerpc/include/asm/nvram.h and use the cross-platform static functions
in linux/nvram.h instead.

Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/nvram.h

@@ -15,8 +15,11 @@ extern const struct nvram_ops arch_nvram_ops;
 
 static inline ssize_t nvram_get_size(void)
 {
+#ifdef CONFIG_PPC
+#else
 	if (arch_nvram_ops.get_size)
 		return arch_nvram_ops.get_size();
+#endif
 	return -ENODEV;
 }