ldscripts: Move mulle.ld into separate dir.

Will add split version of the ldscript as well.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
ldscripts: Update mulle.ld with C++ etc.

This version is based on the modular version in the Contiki repo [1].
This ldscript should fit C++ code as well as C code, although it is
still untested.

The startcode has been updated to match the reversed _stack_start and
_stack_end symbols.

See also:
https://github.com/eistec/contiki/tree/mulle-2-7/cpu/arm/k60/ldscripts

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
ldscripts: Added modular version from Contiki.

This is taken straight from our Contiki port. This is a modularised
version of the ldscript, for easier maintainability of multiple
processor variations. Currently the MK60DN256VLL10 and the
MK60DN512VLL10 are supported. The same linker scripts support both 1.x
and 2.x version silicon (MK60DN256ZVLL10 vs. MK60DN256VLL10, no Z)

See also:
https://github.com/eistec/contiki/tree/mulle-2-7/cpu/arm/k60/ldscripts

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
ldscripts: Add README.md

Added a README explaining which file to use and why it is needed.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
ldscripts: Add more instructions to README.md.

Added example LDFLAGS for using both monolithic and modular ldscripts.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>