It's a pain for architecture maintainers to keep the toplevel Kconfig
files in sync.  This addresses part of the problem by moving all the
standard driver includes to drivers/Kconfig.  As a bonus, it moves all
the device drivers together in a menu which tames menuconfig somewhat.

This patch only touches i386.  Other architectures can join the party
as soon as they feel ready to inflict all the choices on their userbase.