Dgemm loop unroll and 4x1, 4x2 dgemv VSX implementation for power10. #6195

Job	Run time
msys2 (CLANG64, int32, Release)	21m 57s
msys2 (MINGW32, int32, Release)	15m 36s
build (ubuntu-latest, flang, cmake)	9m 53s
msys2 (UCRT64, int64, Release)	15m 50s
msys2 (UCRT64, int32, Release)	16m 21s
msys2 (UCRT64, int32, None, mingw-w64-ucrt-x86_64, fc)	13m 27s
msys2 (CLANG64, int64, Release)	19m 2s
build (ubuntu-latest, gfortran, make)	21m 39s
build (ubuntu-latest, flang, make)	7m 2s
build (macos-latest, gfortran, cmake)	35m 1s
build (ubuntu-latest, gfortran, cmake)	47m 0s
build (macos-latest, gfortran, make)	9m 35s
cross_build (mipsel, mipsel-linux-gnu, TARGET=MIPS1004K)	5m 20s
cross_build (mips64el, mips64el-linux-gnuabi64, DYNAMIC_ARCH=1 TARGET=GENERIC)	4m 4s
cross_build (riscv64, riscv64-linux-gnu, TARGET=RISCV64_GENERIC)	3m 39s
cross_build (alpha, alpha-linux-gnu, TARGET=EV4)	3m 4s
neoverse_build	7m 45s
	4h 16m 15s

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