ext-toolchain-wrapper: fix uboot/linux with hardfp

The linux kernel and uboot specify -msoft-float in order to prevent floating
point code from being generated.  This causes a conflict when -mfloat-abi=hard
or -mfloat-abi options are specified in the wrapper. This patch removes the
-mfloat-abi option from the options generated by the wrapper only when
-msoft-float, -mhard-float or -mfloat-abi are specified by the user.

[Peter: fix !BR_FLOAT_ABI case, simplify]
Signed-off-by: Spenser Gilliland <spenser@gillilanding.com>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>