test/arch/{ecp5,ice40}/memories.ys: Use read_verilog -defer.

test/arch/{ecp5,ice40}/memories.ys: Use read_verilog -defer.

These parts keep rereading a Verilog module, then using chparam
to test it with various parameter combinations.  Since the default
parameters are on the large side, this spends a lot of time
needlessly elaborating the default parametrization that will then
be discarded.  Fix it with -deref and manual hierarchy call.

Shaves 30s off the test time on my machine.