Only use non-blocking assignments of SB_RAM40_4K for yosys

Only use non-blocking assignments of SB_RAM40_4K for yosys

In an initial statement, blocking assignments are normally used
and e.g. verilator throws a warning if non-blocking ones are used.

Yosys cannot however properly resolve the interdependencies if
blocking assignments are used in the initialization of SB_RAM_40_4K
and thus this has been used.

This patch will change to use non-blocking assignments only for yosys