modules/zstd: now included by default. Deactivated under legacy-flash boards

Rationale:
cpio -t alone cannot extract initrd past early cpio (microcode) in most packed initrd.
unpack_initramfs.sh already under master comes to the rescue, but its usage up to today was limited to pass firmware blobs to final OS under boards/librem_mini_v2

Debian OSes (and probably others) need to have cryptroot/crypttab overriden directly, otherwise generic generation of crypttab is not enough.
Extracting crypttab and overriding directly what is desired by final OS and exposed into /boot/initrd is the way to go otherwise hacking on top of hacks.

This brings default packed modules under Heads to 5 modules, which needs to be deactivate in board configs if undesired:
user@heads-tests-deb12:~/heads$ grep -Rn "?= y" modules/ | grep -v MUSL
modules/zlib:1:CONFIG_ZLIB ?= y
modules/zstd:3:CONFIG_ZSTD ?= y
modules/exfatprogs:2:CONFIG_EXFATPROGS ?= y
modules/busybox:2:CONFIG_BUSYBOX ?= y
modules/e2fsprogs:2:CONFIG_E2FSPROGS ?= y

Author: tlaurion

boards/UNTESTED_t430-legacy-flash/UNTESTED_t430-legacy-flash.config

@@ -13,6 +13,7 @@ CONFIG_LINUX_CONFIG=config/linux-x230-flash.config
 #Add bare minimal tools for flashing boards
 CONFIG_BASH=n
 CONFIG_FLASHROM=y
+CONFIG_ZSTD=n
 #CONFIG_GPG=y
 #CONFIG_FLASHTOOLS=y
 CONFIG_PCIUTILS=y

boards/librem_mini_v2/librem_mini_v2.config

@@ -20,8 +20,6 @@ CONFIG_PCIUTILS=y
 CONFIG_POPT=y
 CONFIG_QRENCODE=y
 CONFIG_TPMTOTP=y
-# zstd-decompress - for blob jail, needed to extract /init from zstd cpio archive
-CONFIG_ZSTD=y
 
 CONFIG_CAIRO=y
 CONFIG_FBWHIPTAIL=y

boards/x230-legacy-flash/x230-legacy-flash.config

@@ -13,6 +13,7 @@ CONFIG_LINUX_CONFIG=config/linux-x230-flash.config
 #Add bare minimal tools for flashing boards
 CONFIG_BASH=n
 CONFIG_FLASHROM=y
+CONFIG_ZSTD=n
 #CONFIG_GPG=y
 #CONFIG_FLASHTOOLS=y
 CONFIG_PCIUTILS=y
@@ -21,6 +22,7 @@ CONFIG_PCIUTILS=y
 #CONFIG_TPMTOTP=y
 #CONFIG_DROPBEAR=y
 
+
 #Additional hardware support
 CONFIG_LINUX_USB=y
 #CONFIG_LINUX_E1000E=y

modules/zstd

@@ -1,3 +1,6 @@
+# ZSTD is always included, unless explicitly turned off
+# Needed by initrd/bin/unpack_initramfs.sh under TPM Disk Unlock Key setup
+CONFIG_ZSTD ?= y
 modules-$(CONFIG_ZSTD) += zstd
 
 zstd_version := 1.5.5