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/ls1046ardb_sdcard_defconfig b/configs/ls1046ardb_sdcard_defconfig
index 0ea465c..b0302ef 100644
--- a/configs/ls1046ardb_sdcard_defconfig
+++ b/configs/ls1046ardb_sdcard_defconfig
@@ -30,6 +30,7 @@
 CONFIG_BOOTDELAY=10
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 root=/dev/ram0 earlycon=uart8250,mmio,0x21c0500 mtdparts=1550000.spi-0:1m(rcw),15m(u-boot),48m(kernel.itb);7e800000.flash:16m(nand_uboot),48m(nand_kernel),448m(nand_free)"
+CONFIG_BOOTCOMMAND="run distro_bootcmd;run sd_bootcmd; env exists secureboot && esbc_halt;"
 CONFIG_MISC_INIT_R=y
 CONFIG_SPL_FSL_PBL=y
 CONFIG_SPL_BOARD_INIT=y