rtc: add rtc command

Mostly as an aid for debugging RTC drivers, provide a command that can
be used to read/write arbitrary registers (assuming the driver
provides the read/write methods or their single-register-at-a-time
variants).

Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
diff --git a/cmd/Makefile b/cmd/Makefile
index 7008dd4..dc412d1 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -122,6 +122,7 @@
 obj-$(CONFIG_CMD_REMOTEPROC) += remoteproc.o
 obj-$(CONFIG_CMD_RNG) += rng.o
 obj-$(CONFIG_CMD_ROCKUSB) += rockusb.o
+obj-$(CONFIG_CMD_RTC) += rtc.o
 obj-$(CONFIG_SANDBOX) += host.o
 obj-$(CONFIG_CMD_SATA) += sata.o
 obj-$(CONFIG_CMD_NVME) += nvme.o