ACPI: LPSS: Add pwm_lookup_table entry for second PWM on CHT/BSW devices

BSW PWM2 is used for backlight control for fixed (etched into the glass)
touch controls on some models.

Add an entry for the second PWM controller to bsw_pwm_lookup,
so that drivers can use pwm_get() to get a reference to it.

These touch-controls have specialized drivers which bind to different
devices on different models, so the consumer-device-name in the lookup
table entry is set to NULL, so that only con-id matching is used.

The con-id is set to "pwm_soc_lpss_2" which describes the PWM controller
rather than the usual approach of describing its function.
The specialized (model specific) drivers which need access to the PWM
controller know they need the "pwm_soc_lpss_2" con-id.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>