Use PROJECT-u-boot-VERSION-DATE.bin as u-boot target

Provide link using "u-boot.bin"

Add BR2_TARGET_UBOOT_DEFAULT_ENV config
If this is set, Buildroot will generate
a default environment to allow easy downloading
of the kernel and root file system
Both as compile time data and an autoscript.

Make u-boot depend on $(U_BOOT_TARGETS)
Add "u-boot-autoscript" to U_BOOT_TARGETS if 
BR2_TARGET_UBOOT_DEFAULT_ENV is set.

Take kernel name from Linux build.

Use correct ARCH when mkimaging the autoscript.
Do not use TARGET_ATMEL_COPYTO for generic u-boot.

Hide dataflash memory configurations when 
different boot memory is used.