Move conditional compilation of MPC8XXX SPI driver to Makefile

Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
diff --git a/include/spi.h b/include/spi.h
index 7744c2e..320e50e 100644
--- a/include/spi.h
+++ b/include/spi.h
@@ -24,6 +24,15 @@
 #ifndef _SPI_H_
 #define _SPI_H_
 
+/* Controller-specific definitions: */
+
+/* CONFIG_HARD_SPI triggers SPI bus initialization in PowerPC */
+#ifdef CONFIG_MPC8XXX_SPI
+# ifndef CONFIG_HARD_SPI
+#  define CONFIG_HARD_SPI
+# endif
+#endif
+
 /* SPI mode flags */
 #define	SPI_CPHA	0x01			/* clock phase */
 #define	SPI_CPOL	0x02			/* clock polarity */