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/P2020RDB-PC_36BIT_SDCARD_defconfig b/configs/P2020RDB-PC_36BIT_SDCARD_defconfig
index 6f421ac..e69a5cf 100644
--- a/configs/P2020RDB-PC_36BIT_SDCARD_defconfig
+++ b/configs/P2020RDB-PC_36BIT_SDCARD_defconfig
@@ -20,6 +20,8 @@
 CONFIG_OF_STDOUT_VIA_ALIAS=y
 CONFIG_SYS_EXTRA_OPTIONS="SDCARD"
 CONFIG_BOOTDELAY=10
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="setenv bootargs root=/dev/$bdev rw rootdelay=30 console=$consoledev,$baudrate $othbootargs;usb start;ext2load usb 0:1 $loadaddr /boot/$bootfile;ext2load usb 0:1 $fdtaddr /boot/$fdtfile;bootm $loadaddr - $fdtaddr"
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_BOARD_EARLY_INIT_R=y
 # CONFIG_MISC_INIT_R is not set