icebox_hlc2asc: Allow truth tables to be specified as init string.
icebox_hlc2asc: Allow truth tables to be specified as init string.

Examples;
```hlc
lutff_5 {
    # - Parameters -------
    # LUT_INIT = 0111111110000000

    local_g3_4 -> lutff_5/in_0
    local_g0_6 -> lutff_5/in_1
    local_g2_7 -> lutff_5/in_2
    lutff_5/out -> span4_x3_g12_11
    lutff_5/out -> local_g3_5 -> lutff_5/in_3
    out = 16'b0111111110000000
    enable_dff
}
```

```hlc
lutff_4 {
    local_g3_5 -> lutff_4/in_2
    lutff_4/out -> span12_y12_g6_0
    out = 16'b0000000000010000
    enable_dff
}
```

```hlc
lutff_2 {
    # - Parameters -------
    # LUT_INIT = 01

    lutff_2/out -> span12_y12_g8_0
    lutff_2/out -> span12_x2_g14_0
    lutff_2/out -> local_g0_2 -> lutff_2/in_0
    out = 2'b01
    enable_dff
}
```

SymbiFlow/icestorm,SymbiFlow/icestorm,SymbiFlow/icestorm,SymbiFlow/icestorm