In the images generated by Gowin IDE, the signals for dynamic BSRAM
block selection (BLKSEL[2:0]) are not always connected directly to the
ports - some chips add LUT2, LUT3 or LUT4 to turn these signals into
Clock Enable. Apparently there are chips with an error in the operation
of these ports.
Here we make such a decoder instead of using ports directly.
Signed-off-by: YRabbit <rabbit@yrabbit.cyou>