Fix bf16->f32 conversion for NEOVERSEV1 and NEOVERSEN2 targets #6145

Job	Run time
msys2 (UCRT64, int32, None, mingw-w64-ucrt-x86_64, fc)	15m 39s
msys2 (MINGW32, int32, Release)	15m 33s
build (ubuntu-latest, gfortran, make)	22m 36s
msys2 (CLANG64, int64, Release)	18m 37s
build (macos-latest, gfortran, cmake)	20m 47s
msys2 (CLANG64, int32, Release)	18m 17s
msys2 (UCRT64, int64, Release)	17m 12s
build (macos-latest, gfortran, make)	13m 59s
msys2 (UCRT64, int32, Release)	15m 14s
build (ubuntu-latest, flang, cmake)	11m 42s
neoverse_build	8m 1s
cross_build (riscv64, riscv64-linux-gnu, TARGET=RISCV64_GENERIC)	2m 46s
cross_build (mips64el, mips64el-linux-gnuabi64, DYNAMIC_ARCH=1 TARGET=GENERIC)	3m 36s
cross_build (alpha, alpha-linux-gnu, TARGET=EV4)	3m 2s
build (ubuntu-latest, flang, make)	5m 13s
cross_build (mipsel, mipsel-linux-gnu, TARGET=MIPS1004K)	3m 50s
build (ubuntu-latest, gfortran, cmake)	45m 57s
	4h 2m 1s

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