pwm: lpss: Actually use a module namespace by defining the namespace earlier

DEFAULT_SYMBOL_NAMESPACE must be already defined when <linux/export.h>
is included. So move the define above the include block.

With the DEFAULT_SYMBOL_NAMESPACE being defined too late, the exported
symbols end up in the default namespace. So the respective modules can
use the symbols defined in pwm-lpss.c just fine and up to now just
imported the PWM_LPSS namespace without any gain.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>