hwf-arm: fix incorrect HWCAP2 for SHA1 and SHA2 on AArch32

* src/hwf-arm.c (HWCAP2_SHA1, HWCAP2_SHA2): Change from bit indexes to
flags.

Bachported-from-master: 6b6bfd57d0a6b2b4577c084db35078cd9fadafa5

• GnuPG-bug-id: T5195
• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>