[Libre-soc-dev] change sv ld/st to allow non-zero immediates for unit-strided load/store

[Jacob Lifshay]

this will be very common in spill code or other code with vectors stored in
a struct or on stack:
sv.ld/unitstrided *r120, -32(r1) # load from local stack var in redzone
sv.ld/unitstrided *r32, 64(r1) # load from function arguments
sv.ld/unitstrided *r64, 32(r3) # load from struct member that starts at
offset 32

sorry this is not very detailed, it's 2:30 am here...

Jacob