crash: clean up kdump related config items

By splitting CRASH_RESERVE and VMCORE_INFO out from CRASH_CORE, cleaning
up the dependency of FA_DMUMP on CRASH_DUMP, and moving crash codes from
kexec_core.c to crash_core.c, now we can rearrange CRASH_DUMP to
depend on KEXEC_CORE, and make CRASH_DUMP select CRASH_RESERVE and
VMCORE_INFO.

KEXEC_CORE won't select CRASH_RESERVE and VMCORE_INFO any more because
KEXEC_CORE enables codes which allocate control pages, copy
kexec/kdump segments, and prepare for switching. These codes are shared
by both kexec reboot and crash dumping.

Doing this makes codes and the corresponding config items more
logical (the right item depends on or is selected by the left item).

PROC_KCORE -----------> VMCORE_INFO

           |----------> VMCORE_INFO
FA_DUMP----|
           |----------> CRASH_RESERVE

                                                ---->VMCORE_INFO
                                               /
                                               |---->CRASH_RESERVE
KEXEC      --|                                /|
             |--> KEXEC_CORE--> CRASH_DUMP-->/-|---->PROC_VMCORE
KEXEC_FILE --|                               \ |
                                               \---->CRASH_HOTPLUG

KEXEC      --|
             |--> KEXEC_CORE--> kexec reboot
KEXEC_FILE --|

Link: https://lkml.kernel.org/r/20240124051254.67105-6-bhe@redhat.comSigned-off-by: Baoquan He <bhe@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Hari Bathini <hbathini@linux.ibm.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/Kconfig.kexec

@@ -9,8 +9,6 @@ config VMCORE_INFO
 	bool
 
 config KEXEC_CORE
-	select VMCORE_INFO
-	select CRASH_RESERVE
 	bool
 
 config KEXEC_ELF
@@ -99,8 +97,11 @@ config KEXEC_JUMP
 
 config CRASH_DUMP
 	bool "kernel crash dumps"
+	default y
 	depends on ARCH_SUPPORTS_CRASH_DUMP
-	select KEXEC_CORE
+	depends on KEXEC_CORE
+	select VMCORE_INFO
+	select CRASH_RESERVE
 	help
 	  Generate crash dump after being started by kexec.
 	  This should be normally only set in special crash dump kernels