MIPS: Get rid of CONFIG_CPU_HAS_LLSC again

Commit f7ade3c168e4f437c11f57be012992bbb0e3075c ("MIPS: Get rid of
CONFIG_CPU_HAS_LLSC") did what it promised to do. But since then that
macro and its Kconfig symbol popped up again. Get rid of those again.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Cc: Jonas Gorski <jogo@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/4978/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>