lib/cmdline: Export next_arg() for being used in modules

mainline inclusion
from mainline-v5.13-rc1
commit 65dd36a3
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7TWVA
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=65dd36a39d3b350dc96d8324b348f0863d76404d

-------------------------------------------

At least one module will benefit from using next_arg() helper.
Let's export it for that module and others if they consider it
helpful.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: NLinus Walleij <linus.walleij@linaro.org>
Reviewed-by: NGeert Uytterhoeven <geert+renesas@glider.be>

Conflicts:
	lib/cmdline.c
Signed-off-by: NJinjiang Tu <tujinjiang@huawei.com>

lib/cmdline.c

@@ -253,3 +253,4 @@ char *next_arg(char *args, char **param, char **val)
 	/* Chew up trailing spaces. */
 	return skip_spaces(next);
 }
+EXPORT_SYMBOL(next_arg);