vboot2: remove rsa from vb2_hwcrypto_rsa_allowed

Initially vb2_hwcrypto_rsa_allowed were meant to only determine if we
can use rsa hardware acceleration. However we're planning to also use
this method for hashing, hence drop rsa from the name.

BUG=b:166038345
BRANCH=zork
TEST=CC=x86_64-pc-linux-gnu-clang make runtests

Signed-off-by: Kangheui Won <khwon@chromium.org>
Change-Id: I9efb05b3d035dcd584a47d006415ea87bf931ad6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2566865
Reviewed-by: Joel Kitching <kitching@chromium.org>