LoongArch: Mark {dmw,tlb}_virt_to_page() exports as non-GPL

Mark {dmw,tlb}_virt_to_page() exports as non-GPL, in order to let
out-of-tree modules (e.g. OpenZFS) be built without errors. Otherwise
we get:

ERROR: modpost: GPL-incompatible module zfs.ko uses GPL-only symbol 'dmw_virt_to_page'
ERROR: modpost: GPL-incompatible module zfs.ko uses GPL-only symbol 'tlb_virt_to_page'
Reported-by: Haowu Ge <gehaowu@bitmoe.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/mm/pgtable.c

@@ -13,13 +13,13 @@ struct page *dmw_virt_to_page(unsigned long kaddr)
 {
 	return pfn_to_page(virt_to_pfn(kaddr));
 }
-EXPORT_SYMBOL_GPL(dmw_virt_to_page);
+EXPORT_SYMBOL(dmw_virt_to_page);
 
 struct page *tlb_virt_to_page(unsigned long kaddr)
 {
 	return pfn_to_page(pte_pfn(*virt_to_kpte(kaddr)));
 }
-EXPORT_SYMBOL_GPL(tlb_virt_to_page);
+EXPORT_SYMBOL(tlb_virt_to_page);
 
 pgd_t *pgd_alloc(struct mm_struct *mm)
 {