LoongArch: Fix arch_remove_memory() undefined build error

The kernel build error when unslected CONFIG_MEMORY_HOTREMOVE because
arch_remove_memory() is needed by mm/memory_hotplug.c but undefined.

Some build error messages like:

 LD      vmlinux.o
 MODPOST vmlinux.symvers
 MODINFO modules.builtin.modinfo
 GEN     modules.builtin
 LD      .tmp_vmlinux.kallsyms1
loongarch64-linux-gnu-ld: mm/memory_hotplug.o: in function `.L242':
memory_hotplug.c:(.ref.text+0x930): undefined reference to `arch_remove_memory'
make: *** [Makefile:1169：vmlinux] 错误 1

Removed CONFIG_MEMORY_HOTREMOVE requirement and rearrange the file refer
to the definitions of other platform architectures.
Signed-off-by: Yupeng Li <liyupeng@zbhlos.com>
Signed-off-by: Caicai <caizp2008@163.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/mm/init.c

@@ -131,18 +131,6 @@ int arch_add_memory(int nid, u64 start, u64 size, struct mhp_params *params)
 	return ret;
 }
 
-#ifdef CONFIG_NUMA
-int memory_add_physaddr_to_nid(u64 start)
-{
-	int nid;
-
-	nid = pa_to_nid(start);
-	return nid;
-}
-EXPORT_SYMBOL_GPL(memory_add_physaddr_to_nid);
-#endif
-
-#ifdef CONFIG_MEMORY_HOTREMOVE
 void arch_remove_memory(u64 start, u64 size, struct vmem_altmap *altmap)
 {
 	unsigned long start_pfn = start >> PAGE_SHIFT;
@@ -154,6 +142,16 @@ void arch_remove_memory(u64 start, u64 size, struct vmem_altmap *altmap)
 		page += vmem_altmap_offset(altmap);
 	__remove_pages(start_pfn, nr_pages, altmap);
 }
+
+#ifdef CONFIG_NUMA
+int memory_add_physaddr_to_nid(u64 start)
+{
+	int nid;
+
+	nid = pa_to_nid(start);
+	return nid;
+}
+EXPORT_SYMBOL_GPL(memory_add_physaddr_to_nid);
 #endif
 #endif