LoongArch: Fix Kconfig item and left code related to CRASH_CORE

In commit 85fcde40 ("kexec: split crashkernel reservation code
out from crash_core.c"), crashkernel reservation code is split out from
crash_core.c, and add CRASH_RESERVE to control it. And also rename each
ARCH's <asm/crash_core.h> to <asm/crash_reserve.h> accordingly.

But the relevant part in LoongArch is missed. Do it now.

Fixes: 85fcde40 ("kexec: split crashkernel reservation code out from crash_core.c")
Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/Kconfig

@@ -595,7 +595,7 @@ config ARCH_SELECTS_CRASH_DUMP
 	select RELOCATABLE
 
 config ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
-	def_bool CRASH_CORE
+	def_bool CRASH_RESERVE
 
 config RELOCATABLE
 	bool "Relocatable kernel"

arch/loongarch/include/asm/crash_core.h → arch/loongarch/include/asm/crash_reserve.h

 /* SPDX-License-Identifier: GPL-2.0-only */
-#ifndef _LOONGARCH_CRASH_CORE_H
-#define _LOONGARCH_CRASH_CORE_H
+#ifndef _LOONGARCH_CRASH_RESERVE_H
+#define _LOONGARCH_CRASH_RESERVE_H
 
 #define CRASH_ALIGN			SZ_2M