sha2

sha2: improve RISC-V Zknh backends #1200

Job	Run time
riscv64-zknh	1m 31s
riscv32-zknh	1m 13s
minimal-versions / minimal-versions	36s
set-msrv / set-msrv	2s
macos (1.79.0)	33s
linux (i686-unknown-linux-gnu, 1.79.0, sudo apt update && sudo apt install gcc-multilib)	1m 6s
macos (stable)	29s
cross (1.79.0, aarch64-unknown-linux-gnu, default)	45s
linux (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	59s
build (1.79.0, thumbv7em-none-eabi)	23s
cross (1.79.0, powerpc-unknown-linux-gnu, default)	6m 39s
linux (x86_64-unknown-linux-gnu, 1.79.0)	49s
build (1.79.0, wasm32-unknown-unknown)	24s
cross (stable, aarch64-unknown-linux-gnu, default)	40s
linux (x86_64-unknown-linux-gnu, stable)	39s
windows (1.79.0, x86_64-pc-windows-gnu)	1m 6s
cross (stable, powerpc-unknown-linux-gnu, default)	38s
build (1.79.0, loongarch64-unknown-linux-gnu)	24s
windows (stable, x86_64-pc-windows-gnu)	2m 11s
build (stable, thumbv7em-none-eabi)	18s
build (stable, wasm32-unknown-unknown)	21s
build (stable, loongarch64-unknown-linux-gnu)	29s
	22m 15s

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