kconfig: do not special-case 'MODULES' symbol

Currently, the 'MODULES' symbol is hard-coded to be the default symbol
that enables/disables tristates, if no other symbol was declared with
'option modules'.

While this used to be needed for the Linux kernel, we now have an
explicit 'option modules' attached to the 'MODULES' symbol (since
cset 11097a03

), so we no longer need to special-case it in the
kconfig code.

Furthermore, kconfig is extensively used out of the Linux kernel, and
other projects may have another meaning for a symbol named 'MODULES'.

This patch changes the way we enable/disable tristates: if a symbol was
found with 'option modules' attached to it, then that symbol controls
enabling tristates. Otherwise, tristates are disabled, even if a symbol
named 'MODULES' exists.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>