regulator: qpnp-labibb: Add sysfs class to enable/disable the irq

LAB/IBB interrupts need to be disabled and enabled during the entry and
exit of the secure display use case respectively. Add sysfs property
to allow the userspace to perform this operation

To disable the interrupts:
 echo 1 > /sys/class/lcd_bias/secure_mode

To enable the interrupts:
 echo 0 > /sys/class/lcd_bias/secure_mode.

Change-Id: Iddd5630c0ff6d3191f2cc0d45bd4e72b938728b0
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>
Signed-off-by: Shilpa Suresh <sbsure@codeaurora.org>