Redesign z80 build so that mkhpbase.sh bash script is not needed; remove...

Redesign z80 build so that mkhpbase.sh bash script is not needed; remove support for older SDCC toolchains; Re-verify z80 build on Linux

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5416 42af7a65-404d-4744-a932-0658087f49c3