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/sama5d2_icp_qspiflash_defconfig b/configs/sama5d2_icp_qspiflash_defconfig
index 7722a5e..c1c2298 100644
--- a/configs/sama5d2_icp_qspiflash_defconfig
+++ b/configs/sama5d2_icp_qspiflash_defconfig
@@ -24,6 +24,8 @@
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 earlycon earlyprintk=serial,ttyS0, ignore_loglevel root=/dev/mmcblk0p2 memtest=0 rootfstype=ext4 rw rootwait"
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="fatload mmc 0:1 0x21000000 at91-sama5d2_icp.dtb; fatload mmc 0:1 0x22000000 zImage; bootz 0x22000000 - 0x21000000"
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_MISC_INIT_R=y
 CONFIG_HUSH_PARSER=y