include architecture Kconfig files from top-level Kconfig

[Christoph Hellwig]

Hi Masahiro,

what do you think about the series below, which moves the includes
of all the architecture independ Kconfig files to the top-level
Kconfig instead of duplicating the includes in all architectures?

Note that this only handles the low-hanging fruite, there are a lot
of other bits that should probably be cleaned up to be common,
but those will be not entirely trivial.