i2c: mux: mlxcpld: Move header file out of x86 realm

Move out header file from include/linux/platform_data/x86/ to
include/linux/platform_data/, since it does not depend on x86
architecture.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Michael Shych <michaelsh@nvidia.com>
Acked-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@kernel.org>