Davinci: gpio - minor cleanup

macroized repeated container_of()s to improve readability.
unified direction in/out functions.

Signed-off-by: Cyril Chemparathy <cyril@ti.com>
Tested-by: Sandeep Paulraj <s-paulraj@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>