MFC r306589: Implement iicbus_write_ivar and impelemnt the NOSTOP ivar
in both read and write.

iicbus: Use device_delete_children() instead of explicit child removal

If the bus is detached and deleted by a call to device_delete_child() or
device_delete_children() on a device higher in the tree, I²C children
were already detached and deleted. So the device_t pointer stored in sc
points to freed memory: we must not try to delete it again.

By using device_delete_children(), we let subr_bus.c figure out if there
are children to take care of.

While here, make sure iicbus_detach() and iicoc_detach() call
device_delete_children() too, to be safe.

Reviewed by: jhb, imp
Approved by: jhb, imp
Differential Revision: https://reviews.freebsd.org/D3926

iicbus: Remove trailing whitespaces

MFC of: r289656

MFC r274641, r274644, r274822, r276049:

Allow i2c bus speed to be configured via hints, FDT data, and sysctl.

Implement bus speed setting for OMAP4, AM335x, and imx5/6.

Fix the i2c bus speed divisors for TI OMAP4 and AM335x to give the
advertised 100, 400, and 1000 KHz speeds.

PR: 195009

MFC r274641, r274644, r274822, r276049:

Allow i2c bus speed to be configured via hints, FDT data, and sysctl.

Implement bus speed setting for OMAP4, AM335x, and imx5/6.

Fix the i2c bus speed divisors for TI OMAP4 and AM335x to give the
advertised 100, 400, and 1000 KHz speeds.

PR: 195009