Add support for P4 32X16 RG Bicolor LED Dot Matrix Unit Board

Hello Gaurav,

First of all, thank you so much for writing and publishing HT1632-for-Arduino !

I recently bought a 32X16 RG Bicolor LED Dot Matrix and adapted your codebase
to support it. This board is a bit different in that it uses red+green LEDs. The way
we select the chip is by using a pin (CLK) instead of multiple CSs.

Anyway, I thought it would be useful to folks with that board and I just wanted to
leverage the awesome job you did.

Thanks!

-- flavio