Provide detailed diagnostics in add_children() when DEBUG is
defined ... and fix the non-DEBUG message to include minimal
status, and not appear unless there was actually an error.

Update the IRQ message; have it match what the GPIO subchip
says, and as a precaution, make it only appear if the IRQs
have been initialized.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

Added a few more diagnostics when platform_device_add() fails.
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>