i2c: mux: pca954x: Add ACPI support for pca954x

This patch enables ACPI support for mux-pca954x driver.

Signed-off-by: Tin Huynh <tnhuynh@apm.com>
Acked-by: Peter Rosin <peda@axentia.se>
[wsa: removed a trailing whitespace]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>