declare fpu usage to the assembler in arm hard-float asm files

declare fpu usage to the assembler in arm hard-float asm files

Some armhf gcc toolchains (built with --with-float=hard but without
--with-fpu=vfp*) do not pass -mfpu=vfp to the assembler and then
binutils rejects the UAL mnemonics for VFP unless there is an .fpu vfp
directive in the asm source.