Obsolete support for the 8051 family.  Trying to maintain compatibility with this family is too much effort and there has never really been a successful NuttX impplementation on these parts

Clean up some kernel build heap allocation issues.  The Cortex-A kernel build now compiles without errors (but cannot link until brk() and sbrk() are implemented).

SAMA5D4-EK:  Add a configuration for testing the kernel build configuration (still a work in progress)

Separate flat, protected, and kernel mode library selected into separate files.  The conditional logic as exceed my able to comprehend and maintain the selections.