sha2

sha2: replace `soft` crate feature with configuration flag #1195

Job	Run time
riscv32-zknh	1m 24s
riscv64-zknh	1m 51s
minimal-versions / minimal-versions	34s
set-msrv / set-msrv	4s
macos (1.79.0)	33s
build (1.79.0, thumbv7em-none-eabi)	19s
linux (i686-unknown-linux-gnu, 1.79.0, sudo apt update && sudo apt install gcc-multilib)	57s
macos (stable)	26s
windows (1.79.0, x86_64-pc-windows-gnu)	53s
build (1.79.0, wasm32-unknown-unknown)	21s
linux (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	58s
windows (stable, x86_64-pc-windows-gnu)	1m 17s
build (1.79.0, loongarch64-unknown-linux-gnu)	23s
linux (x86_64-unknown-linux-gnu, 1.79.0)	49s
build (stable, thumbv7em-none-eabi)	13s
linux (x86_64-unknown-linux-gnu, stable)	42s
cross (1.79.0, aarch64-unknown-linux-gnu, default)	57s
build (stable, wasm32-unknown-unknown)	21s
cross (1.79.0, powerpc-unknown-linux-gnu, default)	48s
build (stable, loongarch64-unknown-linux-gnu)	14s
cross (stable, aarch64-unknown-linux-gnu, default)	50s
cross (stable, powerpc-unknown-linux-gnu, default)	34s
	15m 28s

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