ARM: dts: bcm283x: Define standard pinctrl groups in the gpio node.

The BCM2835-ARM-Peripherals.pdf documentation specifies what the
function selects do for the pins, and there are a bunch of obvious
groupings to be made.  With these created, we'll be able to replace
bcm2835-rpi.dtsi's main "set all of these pins to alt0" with
references to specific groups we want enabled.

Also add pinctrl groups for emmc and sdhost.

Based on patches by Eric Anholt, with fixups by Gerd Hoffmann.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>