RFC; Building multiple u-boot images for a single board

[Ulf Samuelsson <ulf.samuelsson@atmel.com>]

If you want to support multiple boot memories, you have to
have multiple boards in the conf/machine directory

I currently testing a change to at91bootstrap, where a defconfig
is not provided by openembedded.
Instead you provide a list of defconfig's in your machine description:

I.E: in conf/machien/at91sam9g45ek.conf you have:

AT91BOOTSTRAP_BOARD = "at91sam9g45df at91sam9g45ek at91sam9g45nf"

when at91bootstrap is built it will loop through all the boards.
and build three versions.

I think it would make sense to do the same for u-boot,
so that you can build u-boot for several configurations.

This change would happen from u-boot-2009.11 an onwards.

In your machine conf you would supply:
UBOOT_MACHINES = "at91sam9g45ekes_nandflash at91sam9g45ekes_dataflash"

A loop goes through the list
and runs make on each element in the list.

make at91sam9g45ekes_nandflash_config
make
make at91sam9g45ekes_dataflash_config
make

if UBOOT_MACHINES is not set, then a single build is done using
UBOOT_MACHINE as usual.

This will allow u_boot to be built for every boot configuration
without having to add a lot of files.

-- 
Best Regards
Ulf Samuelsson