ice40: use 2 bits for READ/WRITE MODE for SB_RAM map
ice40: use 2 bits for READ/WRITE MODE for SB_RAM map

EBLIF output .param will only use necessary 2 bits

Signed-off-by: Elms <93f558a3452e88ebb2324de5c5f48ac5d4ec1d53@freshred.net>

cliffordwolf/yosys,antmicro/yosys,SymbiFlow/yosys,cliffordwolf/yosys,YosysHQ/yosys,YosysHQ/yosys,SymbiFlow/yosys,cliffordwolf/yosys,antmicro/yosys,SymbiFlow/yosys,SymbiFlow/yosys,antmicro/yosys,SymbiFlow/yosys,cliffordwolf/yosys,YosysHQ/yosys,YosysHQ/yosys,antmicro/yosys,YosysHQ/yosys,antmicro/yosys,YosysHQ/yosys,cliffordwolf/yosys,YosysHQ/yosys,cliffordwolf/yosys,cliffordwolf/yosys,YosysHQ/yosys,SymbiFlow/yosys,antmicro/yosys,cliffordwolf/yosys,cliffordwolf/yosys,SymbiFlow/yosys,SymbiFlow/yosys,antmicro/yosys,antmicro/yosys