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/pm9263_defconfig b/configs/pm9263_defconfig
index d2f48e3..c755aaa 100644
--- a/configs/pm9263_defconfig
+++ b/configs/pm9263_defconfig
@@ -15,6 +15,8 @@
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="root=/dev/mtdblock4 rootfstype=jffs2 fbcon=rotate:3 "
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="run flashboot"
 # CONFIG_CONSOLE_MUX is not set
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_BOARD_EARLY_INIT_F=y