CBMEM: Unify get_top_of_ram()

Change-Id: Ic40a51638873642f33c74d80ac41cf082b2fb177
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/3904
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/lib/cbmem.c

@@ -222,7 +222,6 @@ int cbmem_initialize(void)
 	int rv = 0;
 
 #ifdef __PRE_RAM__
-	extern unsigned long get_top_of_ram(void);
 	uint64_t high_tables_base = get_top_of_ram() - HIGH_MEMORY_SIZE;
 	uint64_t high_tables_size = HIGH_MEMORY_SIZE;
 #endif