fs: Convert CONFIG_CMD_CRAMFS to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_CRAMFS

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: imply CMD_CRAMFS for keymile]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/sandbox_spl_defconfig b/configs/sandbox_spl_defconfig
index f22ed39..a8ddb99 100644
--- a/configs/sandbox_spl_defconfig
+++ b/configs/sandbox_spl_defconfig
@@ -60,6 +60,7 @@
 CONFIG_CMD_TPM=y
 CONFIG_CMD_TPM_TEST=y
 CONFIG_CMD_CBFS=y
+CONFIG_CMD_CRAMFS=y
 CONFIG_CMD_EXT4_WRITE=y
 CONFIG_MAC_PARTITION=y
 CONFIG_AMIGA_PARTITION=y