feature-arm-vfp.inc: Further simplify with TUNE_CCARGS_MFLOAT

feature-arm-vfp.inc: Further simplify with TUNE_CCARGS_MFLOAT

* add TUNE_CCARGS_MFLOAT variable which is used to set -mfloat-abi
  parameter as well as ARMPKGSFX_EABI suffix in TUNE_PKGARCH and
  TARGET_FPU
* TARGET_FPU was using ARMPKGSFX_FPU, but in most cases we use it
  only to distinguish between hard and soft abi, not various -mfpu
  variants which can appear in ARMPKGSFX_FPU

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>