LoongArch: Select ARCH_HAS_CURRENT_STACK_POINTER in Kconfig

LoongArch has implemented the current_stack_pointer macro, so select
ARCH_HAS_CURRENT_STACK_POINTER in Kconfig. This will let it be used in
non-arch places (like HARDENED_USERCOPY).

Reviewed-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/Kconfig

@@ -15,6 +15,7 @@ config LOONGARCH
 	select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
 	select ARCH_HAS_ACPI_TABLE_UPGRADE	if ACPI
 	select ARCH_HAS_CPU_FINALIZE_INIT
+	select ARCH_HAS_CURRENT_STACK_POINTER
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS