configs: sandbox: Enable exfat support

Enable exfat support in sandbox and sandbox64 to assure build and
test coverage of this filesystem on both 32bit and 64bit builds.

Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/configs/sandbox64_defconfig b/configs/sandbox64_defconfig
index 7960b2e..1236ce4 100644
--- a/configs/sandbox64_defconfig
+++ b/configs/sandbox64_defconfig
@@ -267,6 +267,7 @@
 CONFIG_WDT_ALARM_SANDBOX=y
 CONFIG_FS_CBFS=y
 CONFIG_FS_CRAMFS=y
+CONFIG_FS_EXFAT=y
 CONFIG_CMD_DHRYSTONE=y
 CONFIG_TPM=y
 CONFIG_ERRNO_STR=y
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 0b3c765..87f21fd 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -352,6 +352,7 @@
 CONFIG_WDT_FTWDT010=y
 CONFIG_FS_CBFS=y
 CONFIG_FS_CRAMFS=y
+CONFIG_FS_EXFAT=y
 CONFIG_ADDR_MAP=y
 CONFIG_PANIC_HANG=y
 CONFIG_CMD_DHRYSTONE=y