mips: add explicit includes of prom.h

In preparation of removing prom.h include by of.h, add explicit includes.
Signed-off-by: NRob Herring <rob.herring@calxeda.com>
Acked-by: NGrant Likely <grant.likely@linaro.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org

arch/mips/lantiq/prom.c

@@ -14,6 +14,7 @@
 
 #include <asm/bootinfo.h>
 #include <asm/time.h>
+#include <asm/prom.h>
 
 #include <lantiq.h>
 

arch/mips/mti-sead3/sead3-setup.c

@@ -10,6 +10,8 @@
 #include <linux/of_fdt.h>
 #include <linux/bootmem.h>
 
+#include <asm/prom.h>
+
 #include <asm/mips-boards/generic.h>
 
 const char *get_system_type(void)

arch/mips/ralink/of.c

@@ -21,6 +21,7 @@
 #include <asm/reboot.h>
 #include <asm/bootinfo.h>
 #include <asm/addrspace.h>
+#include <asm/prom.h>
 
 #include "common.h"