msm: qpnp: Add gpiolib support for PMIC GPIOs

Add a gpio_chip driver to support the Qualcomm SPMI PMIC
architecture called QPNP. The driver supports Device Tree
and allows a device_node to be registered as a gpio-controller.

The driver also specifies APIs to allow a non-Device Tree user
the ability to configure the PMIC GPIOs.

This driver does not handle interrupts for GPIOs directly.
Instead, that work is handled by the existing qpnp-int driver.
This is feasible since the interrupt register map for all
QPNP peripherals is the same.

Change-Id: I04eb39d9855b0957f0647010fcb203ec2fc83c7c
Signed-off-by: Michael Bohan <mbohan@codeaurora.org>