i2c: muxes: pca954x: Add regulator support

Add a vdd regulator and enable it for boards that have the
mux powered off by default.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Acked-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@kernel.org>