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/mx53ppd_defconfig b/configs/mx53ppd_defconfig
index 854d564..71db59f 100644
--- a/configs/mx53ppd_defconfig
+++ b/configs/mx53ppd_defconfig
@@ -14,6 +14,8 @@
 CONFIG_SUPPORT_RAW_INITRD=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_BOOTDELAY=1
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="run doquiet; run tryboot"
 # CONFIG_CONSOLE_MUX is not set
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y