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/pcm058_defconfig b/configs/pcm058_defconfig
index ce7be03..b30270a 100644
--- a/configs/pcm058_defconfig
+++ b/configs/pcm058_defconfig
@@ -27,7 +27,7 @@
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_FIT=y
 CONFIG_BOOTDELAY=3
-# CONFIG_USE_BOOTCOMMAND is not set
+CONFIG_BOOTCOMMAND="run mmcboot;run nandboot"
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_SPL_BOARD_INIT=y
 CONFIG_SPL_SEPARATE_BSS=y