flags: added flag definitions.

* Added definitions of the gpio_pin_info::flags field to
  gpio-core.h.

Signed-off-by: Michel Megens <dev@michelmegens.net>
irq: splitted the state and value field.

* The state of the pin and its value are now saved in two different
  data fields. The state of the pin is (obviously) stored in
  gpio_irq_data::state and the value is (again, obviously) stored in
  the gpio_irq_data::value field.

Signed-off-by: Michel Megens <dev@michelmegens.net>
Merge branch 'doc'
Merge pull request #2 from bietje/master

Merge of branch doc into master.