scripts: introduce float type as a string

With the upcoming softfp support, the case..esac test would become
a bit convoluted if it were to test three different booleans.

Introduce a new blind string config option that defaults to the
selected floating point type used.

Signed-off-by: Michael Hope <michael.hope@linaro.org>
[yann.morin.1998@anciens.enib.fr: split the original patch]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 source "config/configure.in"

 source "config/backend.in"

 source "config/global.in"

 source "config/target.in"

 source "config/toolchain.in"

 source "config/kernel.in"

 source "config/binutils.in"

 source "config/cc.in"

 source "config/libc.in"

 source "config/debug.in"

 source "config/companion_libs.in"

 source "config/companion_tools.in"

 source "config/test_suite.in"