LoongArch: Add Kconfig option AS_HAS_EXPLICIT_RELOCS

GNU as >= 2.40 and GCC >= 13 will support using explicit relocation
hints in the assembly code, instead of la.* macros. The usage of
explicit relocation hints can improve code generation so it's enabled
by default by GCC >= 13.

Introduce a Kconfig option AS_HAS_EXPLICIT_RELOCS as the switch for
"use explicit relocation hints or not".
Tested-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/Kconfig

@@ -195,6 +195,9 @@ config SCHED_OMIT_FRAME_POINTER
 	bool
 	default y
 
+config AS_HAS_EXPLICIT_RELOCS
+	def_bool $(as-instr,x:pcalau12i \$t0$(comma)%pc_hi20(x))
+
 menu "Kernel type and options"
 
 source "kernel/Kconfig.hz"