Update Buildroot (and everything)

There are several important updates:

- Buildroot now contains patches for per-package shared dirs, which is a
prerequisute for top-level parallel build. We're making heavy use of
that one.

- Buildroot has some semi-broken support for sysrepo. I've sent our
improvements upstream earlier today. Some changes are a bit more
granular (the C++ bindings for example).

- This also updated a bunch of packages, of course.

- Our systemd patch required updating, let's see if this one works well
under all circumstances.

Also update some docs as we're rebuilding anyway...

Change-Id: I816fc6105eb999b7b582527ff3540d7a6d634679
diff --git a/configs/czechlight_clearfog_defconfig b/configs/czechlight_clearfog_defconfig
index cd9ce8c..8126a8b 100644
--- a/configs/czechlight_clearfog_defconfig
+++ b/configs/czechlight_clearfog_defconfig
@@ -25,7 +25,7 @@
 BR2_ROOTFS_POST_SCRIPT_ARGS="-c $(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/genimage.cfg"
 BR2_LINUX_KERNEL=y
 BR2_LINUX_KERNEL_CUSTOM_VERSION=y
-BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="5.0"
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="5.4.1"
 BR2_LINUX_KERNEL_PATCH="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/patches/linux.patch"
 BR2_LINUX_KERNEL_DEFCONFIG="mvebu_v7"
 BR2_LINUX_KERNEL_CONFIG_FRAGMENT_FILES="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/linux.fragment $(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/common/linux.fragment"
@@ -44,11 +44,15 @@
 BR2_PACKAGE_PMBUS_PEEK=y
 BR2_PACKAGE_SPI_TOOLS=y
 BR2_PACKAGE_UBOOT_TOOLS=y
+BR2_PACKAGE_LIBSSH=y
+BR2_PACKAGE_LIBSSH_SERVER=y
 BR2_PACKAGE_LIBGPIOD_TOOLS=y
 BR2_PACKAGE_MSTPD=y
+BR2_PACKAGE_NGHTTP2_CXX=y
 BR2_PACKAGE_ETHTOOL=y
 BR2_PACKAGE_IPROUTE2=y
 BR2_PACKAGE_NETCONF_CLI=y
+BR2_PACKAGE_NETOPEER2_CLI=y
 BR2_PACKAGE_TCPDUMP=y
 BR2_PACKAGE_BASH=y
 BR2_PACKAGE_INOTIFY_TOOLS=y