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/imx6q_logic_defconfig b/configs/imx6q_logic_defconfig
index 96736f9..54029ad 100644
--- a/configs/imx6q_logic_defconfig
+++ b/configs/imx6q_logic_defconfig
@@ -23,7 +23,7 @@
 CONFIG_LTO=y
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_BOOTDELAY=3
-# CONFIG_USE_BOOTCOMMAND is not set
+CONFIG_BOOTCOMMAND="run autoboot"
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y
 CONFIG_SPL_RAW_IMAGE_SUPPORT=y