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/imx28_xea_defconfig b/configs/imx28_xea_defconfig
index 63ab834..249bdd6 100644
--- a/configs/imx28_xea_defconfig
+++ b/configs/imx28_xea_defconfig
@@ -26,6 +26,8 @@
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyAMA0,115200n8"
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="run ${bootpri} ; run ${bootsec}"
 CONFIG_USE_PREBOOT=y
 CONFIG_PREBOOT="run prebootcmd"
 CONFIG_BOARD_EARLY_INIT_F=y