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>

examples/standalone/mips64.lds

@@ -0,0 +1,59 @@
+/*
+ * (C) Copyright 2003
+ * Wolfgang Denk Engineering, <wd@denx.de>
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+/*
+OUTPUT_FORMAT("elf32-bigmips", "elf32-bigmips", "elf32-bigmips")
+*/
+OUTPUT_FORMAT("elf64-tradbigmips", "elf64-tradbigmips", "elf64-tradlittlemips")
+OUTPUT_ARCH(mips)
+SECTIONS
+{
+	.text       :
+	{
+	  *(.text*)
+	}
+
+	. = ALIGN(4);
+	.rodata  : { *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*))) }
+
+	. = ALIGN(4);
+	.data  : { *(.data*) }
+
+	. = .;
+	_gp = ALIGN(16) + 0x7ff0;
+
+	.got : {
+	  __got_start = .;
+	  *(.got)
+	  __got_end = .;
+	}
+
+	.sdata  : { *(.sdata*) }
+
+	. = ALIGN(4);
+	__bss_start = .;
+	.sbss (NOLOAD) : { *(.sbss*) }
+	.bss (NOLOAD)  : { *(.bss*) . = ALIGN(4); }
+
+	_end = .;
+}