LoongArch: Automatically disable kaslr if boot from kexec_file

Automatically disable kaslr when the kernel loads from kexec_file.

kexec_file loads the secondary kernel image to a non-linked address,
inherently providing KASLR-like randomization.

However, on LoongArch where System RAM may be non-contiguous, enabling
KASLR for the second kernel may relocate it to an invalid memory region
and cause a boot failure. Thus, we disable KASLR when "kexec_file" is
detected in the command line.

To ensure compatibility with older kernels loaded via kexec_file, this
patch should be backported to stable branches.

Cc: stable@vger.kernel.org
Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>