[PATCH 2/3] [v8] pinctrl: qcom: disable GPIO groups with no pins

On 12/13, Timur Tabi wrote:

pinctrl-msm only accepts an array of GPIOs from 0 to n-1, and it expects
each group to support have only one pin (npins == 1).

We can support "sparse" GPIO maps if we allow for some groups to have zero
pins (npins == 0).  These pins are "hidden" from the rest of the driver
and gpiolib.

Access to unavailable GPIOs is blocked via a request callback.  If the
requested GPIO is unavailable, -EACCES is returned, which prevents
further access to that GPIO.

Signed-off-by: Timur Tabi <redacted>
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Reviewed-by: Stephen Boyd <redacted>

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