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/M5275EVB_defconfig b/configs/M5275EVB_defconfig
index aed36ce..3cb77b7 100644
--- a/configs/M5275EVB_defconfig
+++ b/configs/M5275EVB_defconfig
@@ -7,6 +7,8 @@
 CONFIG_TARGET_M5275EVB=y
 CONFIG_SYS_LOAD_ADDR=0x800000
 CONFIG_BOOTDELAY=5
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="bootm ffe40000"
 # CONFIG_DISPLAY_BOARDINFO is not set
 # CONFIG_CMDLINE_EDITING is not set
 # CONFIG_AUTO_COMPLETE is not set