twl4030-core: portability updates

Improve handling of the OMAP-specific setup in twl4030-core,
and remove various warnings on non-OMAP builds.

The main remaining portability problem for this core code (from
a build perspective) is needing symbols like TWL4030_PWR_IRQ_BASE
which are undesirable and platform-specific.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>