cmd: Split out timer command from the sleep command

CONFIG_CMD_TIMER merits a single file instead of co-exist in the
sleep command file.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
diff --git a/cmd/Makefile b/cmd/Makefile
index 70fe52b..c617474 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -141,6 +141,7 @@
 obj-$(CONFIG_CMD_SYSBOOT) += sysboot.o pxe_utils.o
 obj-$(CONFIG_CMD_TERMINAL) += terminal.o
 obj-$(CONFIG_CMD_TIME) += time.o
+obj-$(CONFIG_CMD_TIMER) += timer.o
 obj-$(CONFIG_CMD_TRACE) += trace.o
 obj-$(CONFIG_HUSH_PARSER) += test.o
 obj-$(CONFIG_CMD_TPM) += tpm-common.o