fs: btrfs: add zstd decompression support

This adds decompression support for Zstandard, which has been included
in Linux btrfs driver for some time.

Signed-off-by: Marek BehĂșn <marek.behun@nic.cz>
diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
index 22909d9..f302b1f 100644
--- a/fs/btrfs/Kconfig
+++ b/fs/btrfs/Kconfig
@@ -2,6 +2,7 @@
 	bool "Enable BTRFS filesystem support"
 	select CRC32C
 	select LZO
+	select ZSTD
 	select RBTREE
 	help
 	  This provides a single-device read-only BTRFS support. BTRFS is a