ARM: dts: bcm283x: Use GPIO polarity defines consistently

Currently most of the Raspberry Pi DTS have a mixture of magic
numbers and the proper GPIO polarity defines. So use the latter
one consistently.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>