[coreboot] Kconfig: convert dependency lists into HAVE_x properties

[Jens Rottmann]

Hi Stefan,

during doing this I happened to trip over HAVE_HIGH_TABLES, which struck me as really weired:

src/Kconfig:
config HAVE_HIGH_TABLES
	bool
	default y

And various northbridges 'select' this - but what is the point, it defaults to 'y' and has no prompt for the user to unset, so it's _always_ 'y'. So all those 'select's have no effect and can be dropped. Or should it be changed to 'default n'?

And there are the mainboards amd/dbm690t, amd/mahogany, asrock/939a785gmh, all of which do:
config HAVE_HIGH_TABLES
	bool
	default n
	depends on BOARD_...

How can the same config option be defined twice??
These 3 boards say 'default n', but because all 3 have northbridges which do 'select HAVE_HIGH_TABLES', it's _still_ always 'y'.

I really didn't understand what the whole point of this stuff is, so I didn't dare touch it ...

Regards,
Jens