PinePhone: automatically use the right dts in u-boot

@z3ntu wrote in !1143 (comment 322072564):

We also have to think about how we're going to handle the different revisions in the future. I would really dislike to have multiple copies of the pinephone in pmaports just because they need different dtbs to boot.

@DolphinChips wrote:

How about keeping the same package for different revisions but making u-boot script somehow understand what revision of Pinephone it's dealing with and selecting dtb based on that information?

@MartijnBraam wrote:

No the hardware itself has no way to identify the different board revisions sadly

@Minecrell wrote:

If no special handling is needed yet, then we should tell PINE64 to add a way to identify newer revisions in the future. That's what feedback is for IMO :)