hash: Kconfig option for SHA512 hardware acceleration

Commit a479f103 ("hash: Allow for SHA512 hardware implementations")
defined function definitions for hardware accelerated SHA384 and SHA512.
If CONFIG_SHA_HW_ACCEL=y, these functions are used.

We already have boards using CONFIG_SHA_HW_ACCEL=y but none implements the
new functions hw_sha384() and hw_sha512().

For implementing the EFI TCG2 protocol we need SHA384 and SHA512. The
missing hardware acceleration functions lead to build errors on boards like
peach-pi_defconfig.

Introduce a new Kconfig symbol CONFIG_SHA512_HW_ACCEL to control if the
functions hw_sha384() and hw_sha512() shall be used to implement the SHA384
and SHA512 algorithms.

Fixes: a479f103 ("hash: Allow for SHA512 hardware implementations")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

Reviewed-by: Simon Glass <sjg@chromium.org>