powerpc: mpc8xx: Remove usage of common.h

Remove inclusion of common.h and add relevant
includes when necessary.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
diff --git a/arch/powerpc/cpu/mpc8xx/speed.c b/arch/powerpc/cpu/mpc8xx/speed.c
index 1a882a3..baf8138 100644
--- a/arch/powerpc/cpu/mpc8xx/speed.c
+++ b/arch/powerpc/cpu/mpc8xx/speed.c
@@ -4,12 +4,12 @@
  * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
  */
 
-#include <common.h>
 #include <clock_legacy.h>
 #include <mpc8xx.h>
 #include <asm/global_data.h>
 #include <asm/processor.h>
 #include <asm/io.h>
+#include <asm/immap_8xx.h>
 
 DECLARE_GLOBAL_DATA_PTR;