i2c: core: Cleanup I2C ACPI namespace, take 2

I2C ACPI enumeration was originally implemented in another module under
drivers/acpi/ but was later moved into i2c-core with added support for
I2C ACPI operation region.

Rename these acpi_i2c_ prefixed functions, structures and defines in
i2c-core to i2c_acpi_ in order to have more consistent name space.

This is updated version from commit a7003b65 ("i2c: core: Cleanup I2C
ACPI namespace") that got reverted due merge conflicts from
commit 525e6fab ("i2c / ACPI: add support for ACPI reconfigure
notifications").

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>