!766 LoongArch: add kexec&kdump support

Merge Pull Request from: @Hongchen_Zhang 
 


```
This series of patches adds the kexec/kdump feature of the LoongArch
architecture.

The production kernel and capture kernel can be the same kernel with
the same binary implementation added. However, this implementation
depends on the kernel relocation function, so the kernel relocation
implementation and KASLR features are added to this series of patches.

In order to be able to be used normally in machines compatible with the
old interface specification, compatibility with the old interface
specification has also been added.

Manual command line test：
kexec:
 $ sudo kexec -l vmlinuz --reuse-cmdline --initrd=initrd
 $ sudo kexec -e

kdump:
Add crashkernel=512M parameter in grub.cfg,
 $ sudo kexec -p vmlinuz --reuse-cmdline --initrd=initrd
 # echo c > /proc/sysrq-trigger


kdump service mode test:
kexec:
 $ sudo kexec -l vmlinuz --reuse-cmdline --initrd=initrd
 $ sudo kexec -e

kdump:
Add crashkernel=512M parameter in grub.cfg,
 $ sudo systemctl enable kdump
 $ sudo systemctl restart kdump
 # echo c > /proc/sysrq-trigger

```
 
 
Link:https://gitee.com/openeuler/kernel/pulls/766

 

Reviewed-by: Guo Dongtai <guodongtai@kylinos.cn>
Reviewed-by: Jialin Zhang <zhangjialin11@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>