kconfig: use generic macros to implement symbol hashtable

Use helper macros in hashtable.h for generic hashtable implementation.

We can git rid of the hash head index of for_all_symbols().

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kconfig: remove zconf_curname() and zconf_lineno()

Now zconf_curname() and zconf_lineno() are so simple that they just
return cur_filename, cur_lineno, respectively.

Remove these functions, and then use cur_filename and cur_lineno
directly.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kconfig: split menu.c out of parser.y

Compile menu.c as an independent compilation unit.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>