i2c: piix4: Move port I/O region request/release code into functions

Move duplicated region request and release code into a function. Move is
in preparation for following MMIO changes.

Signed-off-by: Terry Bowman <terry.bowman@amd.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
[wsa: added missing curly brace]
Signed-off-by: Wolfram Sang <wsa@kernel.org>