[otbn] Weaken DMEM interface assertions
[otbn] Weaken DMEM interface assertions

These were added in 82d48a9, but aren't necessarily true. For
example (with the code in 3cf9984c1), you can trigger the dmem_addr_o
check with:

  util/dvsim/dvsim.py hw/ip/otbn/dv/uvm/otbn_sim_cfg.hjson \
    -i otbn_single --fixed-seed 2797247331 -w

The final instruction there turns out to be an "SLL x1, x5, x1",
underflowing the call stack.

Anyway, these signals flow to prim_ram_1p_scr where they are ignored
if the request bit isn't set. They don't propagate outside of the OTBN
block.

Signed-off-by: Rupert Swarbrick <290093e2ad2515ed2f14d749293c8cf8e02ca274@lowrisc.org>

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