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

lcdb 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: I9763b788deab448f223ab108d3063f246e138f0e
Signed-off-by: Kavya Nunna <knunna@codeaurora.org>
Signed-off-by: Shilpa Suresh <sbsure@codeaurora.org>