Fix several compile errors for logic added for CONFIG_BUILD_KERNEL, but which cause problems for other configurations

Space at the beginning of the process data space is now reserved for user heap management structures.  In the kernel build mode, these heap structures are shared between the kernel and use code in order to allocate user-specific data.

Fix error in initialize of IDLE TCB due to last change.  The argument list is no long in the TCB, but in the stack.  But not for the IDLE task.  It needs its own mini-argv[] list so that it looks more like other threads.

There used to be two ways to pass parameters to new tasks, depending upon the configuration:  Either (1) argv[] as created as an array with each string strdup'ed.  Or (1) argv[] array and strings were created on the stack before the new task was started.   Now, there is only one way, way (1).  Way (2) might be slightly more compact, but this is not worth carry the complexity of two different ways of doing the same thing.

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