arch: add softfp support

Some architectures support a mixed hard/soft floating point, where
the compiler emits hardware floating point instructions, but passes
the operands in core (aka integer) registers.

For example, ARM supports this mode (to come in the next changeset).

Add support for softfp cross compilers to the GCC and GLIBC
configuration. Needed for Ubuntu and other distros that are softfp.

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>

# SPARC specific config options

## select ARCH_SUPPORTS_32

## select ARCH_SUPPORTS_64

## select ARCH_DEFAULT_32

## select ARCH_USE_MMU

## select ARCH_SUPPORT_CPU

## select ARCH_SUPPORT_TUNE

##

## help The SUN SPARC architecture, as defined by:

## help     32 bit: http://www.sparc.org/standards/V8.pdf

## help     64 bit: http://www.sparc.org/standards/SPARCV9.pdf