cmd: mdc/mwc: normalize disjoint MX_CYCLIC usage

Both CMD_MX_CYCLIC and MX_CYCLIC are in use and defined in Kconfig,
but only the non-CMD version currently does anything. This changes all
usages to prefer the CMD_MX_CYCLIC option (since it's only affecting
addition of the commands), and switches defconfigs using the non-CMD
version to use the CMD version.

Signed-off-by: Joel Johnson <mrjoel@lixil.net>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/bcm958300k_defconfig b/configs/bcm958300k_defconfig
index 11f24ab..6ff9bb7 100644
--- a/configs/bcm958300k_defconfig
+++ b/configs/bcm958300k_defconfig
@@ -12,7 +12,7 @@
 # CONFIG_AUTOBOOT is not set
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_ASKENV=y
-CONFIG_MX_CYCLIC=y
+CONFIG_CMD_MX_CYCLIC=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y