Revert "Avoid initrd and logbuffer area overlaps"

This reverts commit 1b5605ca57
which breaks building on all PPC boards that don't use a log buffer.

include/logbuff.h

@@ -60,7 +60,6 @@ int drv_logbuff_init (void);
 void logbuff_init_ptrs (void);
 void logbuff_log(char *msg);
 void logbuff_reset (void);
-unsigned long logbuffer_base (void);
 
 #endif /* CONFIG_LOGBUFFER */