tests: arch: arm: Use a more common SHA algorithm

The profile type "not set" uses the "default crypto config" header.
However platform may set their own crypto configuration headers.
SHA-512 algorithm is not the most common algorithm to support and
are for example disabled in profile types medium and small.

Change to SHA-256 which is much more common and is even needed
internally by TF-M for protected storage and sub-key derivation.

Update the QEMU icount setting to make the interrupt occur during
the secure call to TF-M.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>