MIPS: Allow MIPS_CPU_SCACHE to be used with different line sizes

CONFIG_MIPS_CPU_SCACHE determines whether to build sc-mips.c.  However,
it is currently hardwired to use an L1_SHIFT of 6 (64 bytes).  Move the
L1_SHIFT selection into the CPU or SoC section so that other SoCs can
select different values.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: f.fainelli@gmail.com
Cc: mbizon@freebox.fr
Cc: jogo@openwrt.org
Cc: jfraser@broadcom.com
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/8162/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>