[oe] Allow choose of U-Boot config for machine

[JH]

Hi,

I am running BitBake Build Tool Core version 1.40.0, originally I
built an image on imx6ullevk booting from SD card, I am building a new
image for a customized i.MX6ULL board booting from NAND. The following
link commented by Otavio Salvador for a patch to allow user to use
UBOOT_CONFIG=nand either in local.conf or command line. Given the
patch was many years old, I think that the current version is able to
support UBOOT_CONFIG=nand either in local.conf or command line, there
is no need to run the patch, is that correct?

http://lists.openembedded.org/pipermail/openembedded-core/2013-August/082284.html

Thank you.

Kind regards,

- JH