ARM: SoC code changes for 6.1

The main changes this time are for the organization of the Kconfig
files, introducing per-vendor top-level options on arm64 to match
those on arm32, and making the platform selection on arm32 more
uniform, in particular for the remaining StrongARM platforms that
still have a couple of special cases compared to the more recent
ones.

I also did a cleanup of the old Footbridge platform, which was
the last holdout for the phys_to_dma()/dma_to_phys() interface
that is now completely gone from arm32, completing work started
by Christoph Hellwig.