arm: zynq: Move bootcommand to defconfig

It will cleanup generic config and enable option to change it for every
board.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/topic_miamiplus_defconfig b/configs/topic_miamiplus_defconfig
index e2d6c93..223dc2e 100644
--- a/configs/topic_miamiplus_defconfig
+++ b/configs/topic_miamiplus_defconfig
@@ -8,6 +8,8 @@
 CONFIG_DEFAULT_DEVICE_TREE="zynq-topic-miamiplus"
 CONFIG_DEBUG_UART=y
 CONFIG_BOOTDELAY=0
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="run $modeboot || run distro_bootcmd"
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_SPL=y
 CONFIG_SPL_STACK_R=y