unbreak allmodconfig KCONFIG_ALLCONFIG=...

	Prior to 3.13 make allmodconfig KCONFIG_ALLCONFIG=/dev/null used
to be equivalent to make allmodconfig; these days it hardwires MODULES to n.
In fact, any KCONFIG_ALLCONFIG that doesn't set MODULES explicitly is
treated as if it set it to n.

	Regression had been introduced by commit cfa98f ("kconfig: do not
override symbols already set"); what happens is that conf_read_simple()
does sym_calc_value(modules_sym) on exit, which leaves SYMBOL_VALID set and
has conf_set_all_new_symbols() skip modules_sym.

	It's pretty easy to fix - simply move that call of sym_calc_value()
into the callers, except for the ones in KCONFIG_ALLCONFIG handling.
Objections?

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: cfa98f2e ("kconfig: do not override symbols already set")
Signed-off-by: Michal Marek <mmarek@suse.com>