cmd: qfw: rename qemu_fw_cfg.[c|h] to qfw.[c|h]

Make file names consistent with CONFIG_QFW and CONFIG_CMD_QFW

Signed-off-by: Miao Yan <yanmiaobest@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/qemu-x86_defconfig b/configs/qemu-x86_defconfig
index a813e5b..45bb3ec 100644
--- a/configs/qemu-x86_defconfig
+++ b/configs/qemu-x86_defconfig
@@ -20,7 +20,7 @@
 # CONFIG_CMD_NFS is not set
 CONFIG_CMD_PING=y
 CONFIG_CMD_TIME=y
-CONFIG_CMD_QEMU_FW_CFG=y
+CONFIG_CMD_QFW=y
 CONFIG_CMD_BOOTSTAGE=y
 CONFIG_CMD_EXT2=y
 CONFIG_CMD_EXT4=y