Added function packRegsForDPTRuse (ruonly).. can be
used as a skeleton by other ports to allocate pointer
registers (HL pair in z80 for example) ..
The example code in device/example/* all pass & the
libraries all build without failure ..would be great if others
can have a got at it ....
Currently only in DS390 port ... will apply this to mcs51
once it is found to be stable ...