Add a bounds verification to the SCL and SDA pin values.

At attach, print the SCL and SDA pin numbers.

Remove a stray blank line.

Remove the GPIOBUS locking from gpioiic_reset(), it is already called with
this lock held.  This fixes a crash when you try to scan the iicbus with
i2c(8).
Ignore IIC_ENOADDR from iicbus_reset() as it only means we have a
master-only controller.

This fixes the iic bus scan with i2c(8) (on supported controllers).

Tested with gpioiic(4).