lib/gcd: Remove use of CPU_NO_EFFICIENT_FFS macro

The CPU_NO_EFFICIENT_FFS pre-processor macro is no longer used, with all
architectures toggling the equivalent Kconfig symbol
CONFIG_CPU_NO_EFFICIENT_FFS instead. Remove our check for the unused
macro.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21046/
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org