Fix mips/mips64 build

 Add _start entry label to mips/mips64 linker begin.S

Change-Id: Idcdfc3391427b53880650798be0583a7ac022bcc
diff --git a/linker/arch/mips/begin.S b/linker/arch/mips/begin.S
index 4a855e6..cbe1e37 100644
--- a/linker/arch/mips/begin.S
+++ b/linker/arch/mips/begin.S
@@ -32,7 +32,9 @@
 
     .ent    __start
     .globl    __start
+    .globl    _start
 __start:
+_start:
     .set    noreorder
     bal    1f
     nop