target-m68k: use floatx80 internally

Coldfire uses float64, but 680x0 use floatx80.
This patch introduces the use of floatx80 internally
and enables 680x0 80bits FPU.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Message-Id: <20170620205121.26515-4-laurent@vivier.eu>
7 files changed