platsupport: Don't require plat/mux.h on all plats

As mux_sys_init is currently required on all Arm platforms, having a
enum definition for all mux features that a platform has requires
defining the enum on all platforms.
We instead replace enum mux_feature with a typedef'd ssize_t and allow
platforms to define enum mux_feature definitions at an implementation
level rather than interface level.

platsupport: use ZF_LOG* instead of custom macros

This commit removes redundant definitions of debug print macros
and replaces them with use of ZF_LOG*.

pragma once and for all

Fix whitespace

- remove trailing whitespace
- remove duplicate blank lines
- remove blank lines at end of file

fix licenses