[U-Boot] U-Boot PXA support

[Alex Sadovsky]

It's slightly off-topic but I wonder whether this ongoing deprecation
of ARMv4 and ARMv5 (first in GCC, then in U-Boot) really simplifies
anything at all.
There are tons of devices that are still working good and there are
even ARMv5-based MCUs that are still produced (such as CH561
manufactured by WCH).

IMHO it makes sense to drop only the XScale-specific tuning first and
to treat PXA (and similar CPUs) as a more generic armv5te. I wonder
what to do when GCC drops ARMv5 completely...