test: compression: add zstd uncompression test

Signed-off-by: Brandon Maier <brandon.maier@collins.com>
diff --git a/configs/sandbox_flattree_defconfig b/configs/sandbox_flattree_defconfig
index 41453e0..f30e806 100644
--- a/configs/sandbox_flattree_defconfig
+++ b/configs/sandbox_flattree_defconfig
@@ -211,6 +211,7 @@
 CONFIG_RSA_VERIFY_WITH_PKEY=y
 CONFIG_TPM=y
 CONFIG_LZ4=y
+CONFIG_ZSTD=y
 CONFIG_ERRNO_STR=y
 # CONFIG_CMD_BOOTEFI_BOOTMGR is not set
 CONFIG_EFI_RUNTIME_UPDATE_CAPSULE=y