gpio: omap: Drop 'method' parameter

The "method" parameter was part of the original port of the driver from
the kernel.  At some point this may have been added to allow for future
differentiation (as omap1 and omap2 have different GPIO IP blocks, so
this wasn't an unreasonable thing to do).  At this point however it's
just extra overhead, so drop.

Signed-off-by: Tom Rini <trini@konsulko.com>