- Copy stable/10@285827 to releng/10.2 in preparation for 10.2-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.2.
- Update default pkg(8) configuration to use the quarterly branch.[1]

Discussed with: re, portmgr [1]
Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r274670, r274671, r276168:

Moves all the duplicate code to a single function.

Verify for invalid modes and unwanted flags before pass the new flags to
driver.

Make gpio_default_map_gpios() static. No functional changes.

Improves the GPIO API description a little bit.

gpio_pin_max must return the maximum supported pin number and not the total
number of pins on the system.

MFC r265012, r265191, r265289, r265310

r265012:
Fix the gpio-specifier decoding by respecting the GPIO controller's
#gpio-cells property.

Add a new ofw_bus method (OFW_BUS_MAP_GPIOS()) that allows the GPIO
controller to implement its own mapping to deal with gpio-specifiers,
allowing the decoding of gpio-specifiers to be controller specific.

The default ofw_bus_map_gpios() decodes the linux standard (#gpio-cells =
<2>) and the FreeBSD standard (#gpio-cells = <3>).

It pass the gpio-specifier flag field to the children as an ivar variable so
they can act upon.

r265191:
Remove unnecessary headers. Sort out the headers. Add a missing header on
ofw_gpiobus.c (it was working because of sys/libkern.h).

r265289:
eally sort out the headers.

sys/systm.h must always come after sys/param.h.

Remove sys/types.h which should never be included together with sys/param.h.

Add sys/malloc.h for correctness even if it seems to don't be needed.

Remove more unused headers found by unusedinc (from bde@).

r265310:
Move gpiobus routines to dev/gpio. Avoid polluting ofw_bus with bus
specific parts.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Initial GPIO bus support. Includes:
- GPIO bus controller interface
- GPIO bus interface
- Implementation of GPIO led(4) compatible device
- Implementation of iic(4) bus over GPIO (author: Luiz Otavio O Souza)

Tested by: Luiz Otavio O Souza, Alexandr Rybalko