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_shc_sdboot_defconfig b/configs/am335x_shc_sdboot_defconfig
index 914f21c..24409b8 100644
--- a/configs/am335x_shc_sdboot_defconfig
+++ b/configs/am335x_shc_sdboot_defconfig
@@ -23,7 +23,7 @@
 CONFIG_AUTOBOOT_PROMPT="Enter 'shc' to enter prompt (times out) %d \nEnter 'noautoboot' to enter prompt without timeout\n"
 CONFIG_AUTOBOOT_DELAY_STR="shc"
 CONFIG_AUTOBOOT_STOP_STR="noautoboot"
-# CONFIG_USE_BOOTCOMMAND is not set
+CONFIG_BOOTCOMMAND="if mmc dev 0; mmc rescan; then run sd_setup; else echo ERROR: SD/MMC-Card not detected!; panic; fi; if run loaduimage; then echo Bootable SD/MMC-Card inserted, booting from it!; run mmcboot; else echo ERROR: Unable to load uImage from SD/MMC-Card!; panic; fi; "
 CONFIG_DEFAULT_FDT_FILE="am335x-shc"
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y