Provide optimized ?SUM kernels for NeoverseN1 and related #1949

Job	Run time
TEST (LOONGSON2K1000, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LOONGSON2K1000)	15m 8s
TEST (LOONGSONGENERIC, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LOONGSONGENERIC)	7m 47s
TEST (LA64_GENERIC, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LA64_GENERIC)	7m 55s
TEST (LA264, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LA264)	7m 56s
TEST (LA464, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LA464)	15m 6s
TEST (LOONGSON3R5, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=LOONGSON3R5)	14m 22s
TEST (DYNAMIC_ARCH, NO_SHARED=1 DYNAMIC_ARCH=1 TARGET=GENERIC)	15m 13s
	1h 23m 27s

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