cmd: mvebu: Rename rx_training to mvebu_comphy_rx_training

Rename the misleading cmd "rx_training" to "mvebu_comphy_rx_training" to
avoid confusion and mixup with DDR3/4 training. This makes it clear,
that this command is platform specific and handles the COMPHY RX
training.

Also depend this cmd on ARMADA_8K and not TARGET_MVEBU_ARMADA_8K to make
is available for OcteonTX2 CN913x.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Pali Rohár <pali@kernel.org>
Cc: Marek Behun <marek.behun@nic.cz>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Nadav Haklai <nadavh@marvell.com>
Acked-by: Marek Behún <marek.behun@nic.cz>
Acked-by: Pali Rohár <pali@kernel.org>
diff --git a/cmd/mvebu/Makefile b/cmd/mvebu/Makefile
index 79299b0..ca96ad0 100644
--- a/cmd/mvebu/Makefile
+++ b/cmd/mvebu/Makefile
@@ -5,4 +5,4 @@
 # https://spdx.org/licenses
 
 obj-$(CONFIG_CMD_MVEBU_BUBT) += bubt.o
-obj-$(CONFIG_CMD_MVEBU_RX_TRAINING) += rx_training.o
+obj-$(CONFIG_CMD_MVEBU_COMPHY_RX_TRAINING) += comphy_rx_training.o