LoongArch: KVM: Compile switch.S directly into the kernel

LoongArch: KVM: Compile switch.S directly into the kernel

If we directly compile the switch.S file into the kernel, the address of
the kvm_exc_entry function will definitely be within the DMW memory area.
Therefore, we will no longer need to perform a copy relocation of the
kvm_exc_entry.

So this patch compiles switch.S directly into the kernel, and then remove
the copy relocation execution logic for the kvm_exc_entry function.

Cc: stable@vger.kernel.org
Signed-off-by: Xianglai Li <lixianglai@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>