drivers/i2c: Use standard bitrate settings for DW driver

Applying the change to relevant arch/boards, either in their Kconfig or
the dts specific files.

Taking the opportunity in dw driver to rename the variable the same way
as they are everywhere else in the code (s/dev/dw and s/port/dev) in
init function.

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>