ppc: Include <asm/cache.h> in common.h

This is needed for the patch "cache: add default setting for
CONFIG_SYS_CACHELINE_SIZE" from Anton Staaf. As cache.h defines
CONFIG_SYS_CACHELINE_SIZE for PPC targets.

This will remove the following warnings/errors:

include/common.h:819:2: warning: #warning CONFIG_SYS_CACHELINE_SIZE not defined, using __BIGGEST_ALIGNMENT__
cache.c:33: error: '__BIGGEST_ALIGNMENT__' undeclared (first use in this function)

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Anton Staaf <robotboy@chromium.org>
Cc: Wolfgang Denk <wd@denx.de>

include/common.h

@@ -782,6 +782,14 @@ int cpu_release(int nr, int argc, char * const argv[]);
 
 #endif /* __ASSEMBLY__ */
 
+#ifdef CONFIG_PPC
+/*
+ * Has to be included outside of the #ifndef __ASSEMBLY__ section.
+ * Otherwise might lead to compilation errors in assembler files.
+ */
+#include <asm/cache.h>
+#endif
+
 /* Put only stuff here that the assembler can digest */
 
 #ifdef CONFIG_POST