add support for GS4_HMSB

As displayio can only show 1 SPI display at a time (because FourWire blocks the SPI bus when 1 display is initialized), I cannot add multiple SSD1327 oleds to my circuitpython project using displayio.
So I have to use framebuf. The SSD1327 oled drivers are GS4_HMSB based. I can get multiple display to work in micropython, but not in circuitpython because framebuf doens't have support for GS4_HMSB.

Would it be possible to add support for this?
I found the c implementation in micropython, but I don't know how to convert this to python language.
see https://github.com/micropython/micropython/blob/master/extmod/modframebuf.c for c implementation.

Start by reading the existing framebuf implementation in this repository and the referenced MicroPython implementation at extmod/modframebuf.c, focusing on GS4_HMSB behavior. Add support for the requested format and verify that SSD1327 displays can use it without breaking existing framebuf formats.

Written by the indexing model from the issue text.