arm: bcmbca: make reset_cpu function weak

BCM63158 carries the CONFIG_SYSRESET from the original configuration. It
provide reset_cpu function already so need to define weak version of the
dummy reset_cpu for other BCMBCA SoCs to avoid linking error.

Signed-off-by: William Zhang <william.zhang@broadcom.com>
Reviewed-by: Philippe Reynes <philippe.reynes@softathome.com>

board/broadcom/bcmbca/board.c

@@ -30,6 +30,6 @@ int print_cpuinfo(void)
 	return 0;
 }
 
-void reset_cpu(ulong addr)
+__weak void reset_cpu(void)
 {
 }