Convert CONFIG_USE_BOOTCOMMAND et al to Kconfig

This converts the following to Kconfig:
   CONFIG_USE_BOOTCOMMAND
   CONFIG_BOOTCOMMAND
   CONFIG_RAMBOOTCOMMAND
   CONFIG_NFSBOOTCOMMAND

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/am335x_baltos_defconfig b/configs/am335x_baltos_defconfig
index 492f7b9..90612e6 100644
--- a/configs/am335x_baltos_defconfig
+++ b/configs/am335x_baltos_defconfig
@@ -14,7 +14,7 @@
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
-# CONFIG_USE_BOOTCOMMAND is not set
+CONFIG_BOOTCOMMAND="run findfdt; run usbboot;run mmcboot;setenv mmcdev 1; setenv bootpart 1:2; run mmcboot;run nandboot;"
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_ARCH_MISC_INIT=y
 CONFIG_SPL_FS_EXT4=y