systemc: Mark some tests as expected to fail.

One of them, systemc/kernel/sc_time/test07, should fail, but it should
fail from an error check and not a floating point exception like it
currently does.

Change-Id: I8c8f3c0aac5a5061780a248bde5f6de2feeecc8c
Reviewed-on: https://gem5-review.googlesource.com/c/12462
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>