Improve vmlinux.lds.h support for arch specific linker scripts

To support alingment of the individual architecture specific linker scripts
provide a set of general definitions in vmlinux.lds.h

With these definitions applied the diverse linekr scripts can be reduced
in line count and their readability are improved - IMO.

A sample linker script is included to give the preferred
order of the sections for the architectures that do not
have any special requirments.

These definitions are also a first step towards eventual
support for -ffunction-sections.
The definitions makes it much easier to do a global
renaming of section names - but the main purpose is
to clean up the linker scripts.

Tim Aboot has provided a lot of inputs to improve
the definitions - all faults are mine.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Tim Abbott <tabbott@mit.edu>