all: Allow multiple config files

This is somewhat an intrusive change, but necessary if we want
to upstream the kdump tooling while allowing great extent of
customizations on SteamOS.

With this change, we have now a kdump.d folder on /usr/share,
that holds configuration files in the same way sysctl.d does.
In other words, we can easily override default settings by
just having more configuration files, which are sourced
following natural name sorting, i.e., we have now the concept
of config file precedence in kdump.

Our default config file is called 00-default, so we eventually
might have a 01-steamos e.g., with Deck's custom settings.
This is planned to other package though.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>

00-default.conf

@@ -0,0 +1,41 @@
+#!/bin/sh
+#
+#  SPDX-License-Identifier: LGPL-2.1+
+#
+#  Copyright (c) 2021 Valve
+#  Maintainer: Guilherme G. Piccoli <gpiccoli@igalia.com>
+#
+#  Configuration settings for kdump/pstore. After _any_ change in this
+#  file, it's required to re-create the kdump minimal initramfs by running:
+#  /usr/lib/kdump/kdump-load.sh initrd
+#
+
+#  Mount-related options - the DEVNODE points to the /home directory link;
+#  this is used to derive the numerical devnode for kdump, since the link
+#  is not present so early in the system boot. The KDUMP_FOLDER will be
+#  created if doesn't exist. The KDUMP_MNT is just a temporary file that
+#  carries the mounted folder path across boot-time scripts.
+
+MOUNT_DEVNODE="/dev/disk/by-partsets/shared/home"
+KDUMP_FOLDER="/.steamos/offload/var/kdump"
+KDUMP_MNT="/tmp/kdump.mnt"
+
+#  Kdump controlling settings - for now we don't have network/iscsi dumps, only
+#  local storage dumps. If FULL_COREDUMP is !=0, we collect a full compressed
+#  vmcore, which might require a lot of disk space. The *_CMD settings refer
+#  to tunings on makedumpfile - we rely on zstd compression and maximum page
+#  exclusion for the full vmcore, mimic'ing Debian kdump. Finally, GRUB_AUTOSET
+#  determines if the kdump tooling should try to automatically set grub.cfg in
+#  order to reserve memory for kdump (if needed, i.e., when pstore is not in
+#  use) - keep it as '1' for enabling the mechanism (this is the default).
+
+FULL_COREDUMP=0
+MAKEDUMPFILE_COREDUMP_CMD="-z -d 31"
+MAKEDUMPFILE_DMESG_CMD="--dump-dmesg"
+GRUB_AUTOSET=1
+
+#  Pstore-RAM setting - if enabled, Kdump won't be loaded, instead the Pstore
+#  RAM backend will be configured. In order to have success, this operation
+#  relies in having an available RAM buffer on /proc/iomem with at least 5MiB
+#  in size.
+USE_PSTORE_RAM=1