Introduce VF610 I2C controller support.

NXP LS1046A contains I2C controller compatible with Vybrid VF610.
Existing Vybrid MVF600 driver can be used to support it. For that purpose
declare driver as ofw_iicbus and add methods associated with ofw_iicbus.

For VF610 add dynamic clock prescaler calculation using clock information
from clock driver and clock frequency requested in device tree.

On the occasion add detach function and add additional error handling
in i2c_attach function.

Submitted by: Dawid Gorecki <dgr@semihalf.com>
Reviewed by: manu
Obtained from: Semihalf
Sponsored by: Alstom Group
Differential Revision: https://reviews.freebsd.org/D24361