x86: Revise appearance of floating point configuration options

Streamlines the prompts and help text for the floating point
configuration options to make them easier to understand. Also
fixes a help text error that said fibers using the floating point
registers needed to provide additional stack space, which is
incorrect.

Change-Id: Ib6fc13460999ec7f737118728a363b4e10d23fcf
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>