MIPS: Hardcode cpu_has_mips* where target ISA allows

In the same vein as commit 93e01942 ("MIPS: Hardcode cpu_has_* where
known at compile time due to ISA"), we can use our knowledge of the ISA
being targeted by the kernel build to make cpu_has_mips* macros
compile-time constant in some cases. This allows the compiler greater
opportunity to optimize out code which will never execute.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21245/
Cc: linux-mips@linux-mips.org