kernel: Clean up of x86 floating point code

Updates x86 floating point support to reflect changes that have
been made in recent months.

* Many, many, many cosmetic changes (mostly revisions to comments).

* Elimination of unnecessary function aliases that were needed
  to support the task and fiber versions of certain APIs.

* Elimination of run-time code to enable a thread's "FP regs"
  option bit if the "SSE regs" option bit was set. The kernel
  now recognizes that the thread is using the FPU as long as
  either option bit is set. (If the thread has both option bits
  enabled this is the same as if only the "SSE regs" bit is set.)

Change-Id: Ic12abc54b6fa78921749b546d8debf23e7ad232d
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>