config/target: enforce floating point support

Do not prompt for the type of floating-point support, if the
architecture did not explicitly stated that it did support it.

Reported-by: Morten Thunberg Svendsen <mts@doredevelopment.dk>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 reporter_name="Bart vdr. Meulen <bartvdrmeulen@gmail.com>"

 reporter_url=""

 reporter_comment="Config to build cross-compiler with mingw as kernel type"