ALSA: core: Enable proc module when CONFIG_MODULES=y

ALSA: core: Enable proc module when CONFIG_MODULES=y

We used '#ifdef MODULE' for judging whether the system supports the
sound module or not, and /proc/asound/modules is created only when
'#ifdef MODULE' is true.  The check is not really appropriate, though,
because the flag means only for the sound core and the drivers are
still allowed to be built as modules even if 'MODULE' is not set in
sound/core/init.c.

For fixing the inconsistency, replace those ifdefs with 'ifdef
CONFIG_MODULES'.  One place for a NULL module check is rewritten with
IS_MODULE(CONFIG_SND) to be more intuitive.  It can't be changed to
CONFIG_MODULES; otherwise it would hit a WARN_ON() incorrectly.

This is a slight behavior change; the modules proc entry appears now
no matter whether the sound core is built-in or not as long as modules
are enabled on the kernel in general.  This can't be avoided due to
the nature of kernel builds.

Link: https://lore.kernel.org/r/20240520170349.2417900-1-xu.yang_2@nxp.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Xu Yang <xu.yang_2@nxp.com>
Link: https://lore.kernel.org/r/20240522070442.17786-2-tiwai@suse.de