libplatsupport,imx: improve CR LF handling

Ensure either CR LF is sent or nothing at all, but never send just a
CR in case the FIFO is full. Add comments about FIFO behavior.

Signed-off-by: Axel Heider <axelheider@gmx.de>

trivial: style fix

Signed-off-by: Axel Heider <axelheider@gmx.de>

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.

util_libs: remove autoconf.h from util_libs

this commit removes autoconf.h generation from each lib and
append '#include <<lib_name>/gen_config.h>' after each
'#include <autoconf.h>' since autoconf.h is only the for the
kernel config now. This is a temporarily solution, since we
currently don't have a way to tell which header files each file
is trying to include when it includes 'autoconf.h'

libplatsupport: Select imx mach drivers by plat

The mach folders contain shared drivers for all platforms with the same
"KernelArmMach" type. Making subdirectories allows for more fine grained
control of source file includes to handle situations when one or more
platforms don't use the shared devices but are still of the same mach.