gpio: qpnp-gpio: Change Device Tree configuration specification

Move to a more flexible means of specififying gpio configuration.
Rather than having one single Device Tree binding override all
configuration options, allow for each parameter to be
overwritten independent of the rest. This allows for a finer
granularity of control. It also gives user friendly names to each
parameter binding so that it's easier to set configuration
values.

Also change qcom,qpnp-gpio-num to qcom,gpio-num. This is more aligned
with the other binding names defined for qpnp-gpio which are not
prepended with qpnp.

Change-Id: I811e1bf93602dddb92bc22a2ba410e9192504d0c
Signed-off-by: Michael Bohan <mbohan@codeaurora.org>