feat: compress amd64 Linux kernel using zstd

This increases the kernel size, but moves us away from xz and improves
decompression speed.

Also enable ZSTD firmware loading (not used yet).

Linux arm64 kernel is compressed with zstd already in 1.8+.

Signed-off-by: Andrey Smirnov <andrey.smirnov@siderolabs.com>

kernel/build/config-amd64

@@ -16,6 +16,7 @@ CONFIG_CC_CAN_LINK_STATIC=y
 CONFIG_CC_HAS_ASM_GOTO_OUTPUT=y
 CONFIG_CC_HAS_ASM_GOTO_TIED_OUTPUT=y
 CONFIG_GCC_ASM_GOTO_OUTPUT_WORKAROUND=y
+CONFIG_TOOLS_SUPPORT_RELR=y
 CONFIG_CC_HAS_ASM_INLINE=y
 CONFIG_CC_HAS_NO_PROFILE_FN_ATTR=y
 CONFIG_PAHOLE_VERSION=126
@@ -42,10 +43,10 @@ CONFIG_HAVE_KERNEL_ZSTD=y
 # CONFIG_KERNEL_GZIP is not set
 # CONFIG_KERNEL_BZIP2 is not set
 # CONFIG_KERNEL_LZMA is not set
-CONFIG_KERNEL_XZ=y
+# CONFIG_KERNEL_XZ is not set
 # CONFIG_KERNEL_LZO is not set
 # CONFIG_KERNEL_LZ4 is not set
-# CONFIG_KERNEL_ZSTD is not set
+CONFIG_KERNEL_ZSTD=y
 CONFIG_DEFAULT_INIT=""
 CONFIG_DEFAULT_HOSTNAME="(none)"
 CONFIG_SYSVIPC=y
@@ -1910,7 +1911,7 @@ CONFIG_EXTRA_FIRMWARE=""
 # CONFIG_FW_LOADER_USER_HELPER is not set
 CONFIG_FW_LOADER_COMPRESS=y
 CONFIG_FW_LOADER_COMPRESS_XZ=y
-# CONFIG_FW_LOADER_COMPRESS_ZSTD is not set
+CONFIG_FW_LOADER_COMPRESS_ZSTD=y
 CONFIG_FW_CACHE=y
 # CONFIG_FW_UPLOAD is not set
 # end of Firmware loader

kernel/build/config-arm64

@@ -1985,7 +1985,7 @@ CONFIG_EXTRA_FIRMWARE=""
 # CONFIG_FW_LOADER_USER_HELPER is not set
 CONFIG_FW_LOADER_COMPRESS=y
 CONFIG_FW_LOADER_COMPRESS_XZ=y
-# CONFIG_FW_LOADER_COMPRESS_ZSTD is not set
+CONFIG_FW_LOADER_COMPRESS_ZSTD=y
 CONFIG_FW_CACHE=y
 # CONFIG_FW_UPLOAD is not set
 # end of Firmware loader