MIPS: Fix ISA level which causes secondary cache init bypassing and more

The commit a96102be introduced set_isa() where compatible ISA info is
also set aside from the one gets passed in. It means, for example, 1004K
will have MIPS_CPU_ISA_M32R2/M32R1/II/I flags. This leads to things like
the following inappropriate:

if (c->isa_level == MIPS_CPU_ISA_M32R1 ||
    c->isa_level == MIPS_CPU_ISA_M32R2 ||
    c->isa_level == MIPS_CPU_ISA_M64R1 ||
    c->isa_level == MIPS_CPU_ISA_M64R2)

This patch fixes it.

Signed-off-by: Deng-Cheng Zhu <dengcheng.zhu@imgtec.com>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>