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/openpiton_riscv64_defconfig b/configs/openpiton_riscv64_defconfig
index 38a3b3f..6dbb079 100644
--- a/configs/openpiton_riscv64_defconfig
+++ b/configs/openpiton_riscv64_defconfig
@@ -14,6 +14,8 @@
 CONFIG_SYS_LOAD_ADDR=0x87000000
 # CONFIG_LEGACY_IMAGE_FORMAT is not set
 # CONFIG_ARCH_FIXUP_FDT_MEMORY is not set
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="fdt addr ${fdtcontroladdr}; fdt move ${fdtcontroladdr} ${fdt_addr_r}; load mmc ${mmcdev}:${mmcpart} ${kernel_addr_r} ${image}; booti ${kernel_addr_r} - ${fdt_addr_r}; "
 CONFIG_SYS_PROMPT="openpiton$ "
 # CONFIG_CMD_CPU is not set
 CONFIG_CMD_BOOTZ=y