MIPS: add board qemu-mips64 support

Both big-endian and little-endian are tested with below commands:
Rom version: (Default, Now we config it as rom version)
qemu-system-mips64el -M mips -bios u-boot.bin -cpu MIPS64R2-generic -nographic
qemu-system-mips64 -M mips -bios u-boot.bin -cpu MIPS64R2-generic -nographic
Ram version:
qemu-system-mips64el -M mips -cpu MIPS64R2-generic -kernel u-boot -nographic
qemu-system-mips64 -M mips -cpu MIPS64R2-generic -kernel u-boot -nographic

Signed-off-by: Zhizhou Zhang <etou.zh@gmail.com>
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/board/qemu-mips/u-boot.lds b/board/qemu-mips/u-boot.lds
index 9460b20..4d9580f 100644
--- a/board/qemu-mips/u-boot.lds
+++ b/board/qemu-mips/u-boot.lds
@@ -24,7 +24,11 @@
 /*
 OUTPUT_FORMAT("elf32-bigmips", "elf32-bigmips", "elf32-bigmips")
 */
+#if defined(CONFIG_64BIT)
+OUTPUT_FORMAT("elf64-tradbigmips", "elf64-tradbigmips", "elf64-tradlittlemips")
+#else
 OUTPUT_FORMAT("elf32-tradbigmips", "elf32-tradbigmips", "elf32-tradlittlemips")
+#endif
 OUTPUT_ARCH(mips)
 ENTRY(_start)
 SECTIONS
@@ -63,7 +67,11 @@
 	}
 
 	uboot_end_data = .;
+#if defined(CONFIG_64BIT)
+	num_got_entries = (__got_end - __got_start) >> 3;
+#else
 	num_got_entries = (__got_end - __got_start) >> 2;
+#endif
 
 	. = ALIGN(4);
 	.sbss  : { *(.sbss*) }