mips: enable O32_FP64 and MSA
CONFIG_MIPS_O32_FP64_SUPPORT is required to support MSA for O32. It requires CPU >= mips32r1. It is OK for us: currently our baseline is mips32r2/mips64r2.
Malta can use different CPUs, some of them may support MSA. Loongson 3A/B 4000 will support MSA. The only CPU currently we support has no MSA is octeon.
Commit-ID in master: b1d08a0c