crash: split vmcoreinfo exporting code out from crash_core.c

Now move the relevant codes into separate files:
kernel/crash_reserve.c, include/linux/crash_reserve.h.

And add config item CRASH_RESERVE to control its enabling.

And also update the old ifdeffery of CONFIG_CRASH_CORE, including of
<linux/crash_core.h> and config item dependency on CRASH_CORE
accordingly.

And also do renaming as follows:
 - arch/xxx/kernel/{crash_core.c => vmcore_info.c}
because they are only related to vmcoreinfo exporting on x86, arm64,
riscv.

And also Remove config item CRASH_CORE, and rely on CONFIG_KEXEC_CORE to
decide if build in crash_core.c.

[yang.lee@linux.alibaba.com: remove duplicated include in vmcore_info.c]
  Link: https://lkml.kernel.org/r/20240126005744.16561-1-yang.lee@linux.alibaba.com
Link: https://lkml.kernel.org/r/20240124051254.67105-3-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Acked-by: Hari Bathini <hbathini@linux.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Pingfan Liu <piliu@redhat.com>
Cc: Klara Modin <klarasmodin@gmail.com>
Cc: Michael Kelley <mhklinux@outlook.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

kernel/ksysfs.c

@@ -154,7 +154,7 @@ KERNEL_ATTR_RW(kexec_crash_size);
 
 #endif /* CONFIG_KEXEC_CORE */
 
-#ifdef CONFIG_CRASH_CORE
+#ifdef CONFIG_VMCORE_INFO
 
 static ssize_t vmcoreinfo_show(struct kobject *kobj,
 			       struct kobj_attribute *attr, char *buf)
@@ -177,7 +177,7 @@ KERNEL_ATTR_RO(crash_elfcorehdr_size);
 
 #endif
 
-#endif /* CONFIG_CRASH_CORE */
+#endif /* CONFIG_VMCORE_INFO */
 
 /* whether file capabilities are enabled */
 static ssize_t fscaps_show(struct kobject *kobj,
@@ -265,7 +265,7 @@ static struct attribute * kernel_attrs[] = {
 	&kexec_crash_loaded_attr.attr,
 	&kexec_crash_size_attr.attr,
 #endif
-#ifdef CONFIG_CRASH_CORE
+#ifdef CONFIG_VMCORE_INFO
 	&vmcoreinfo_attr.attr,
 #ifdef CONFIG_CRASH_HOTPLUG
 	&crash_elfcorehdr_size_attr.attr,