picodvi: support 640x240 and 800x240 (tested @1bpp)

[jepler]

and dynamically calculate dvi_vertical_repeat

the 640x240 mode was useful for a little project of mine

[dhalbert]

Comment on one thing I don't understand.

Could you test this against some existing working cases to check for regression? Thanks.

[dhalbert]

Were you able to test this on an older working test case? Thanks. I just want to make sure there is no regression due to the new code further down in the change.

[jepler]

I tested the following modes:

    {"width":320, "height":240, "color_depth":8},
    {"width":640, "height":240, "color_depth":1}, # (new)
    {"width":640, "height":480, "color_depth":1},
    {"width":800, "height":240, "color_depth":1}, # (new)
    {"width":800, "height":480, "color_depth":1}):

the 400x240@8bpp mode would not initialize:

MemoryError: memory allocation failed, allocating 110412 bytes

This allocation is the framebuffer of 96000 bytes plus the "TDMS buffers":

    size_t total_allocation_size = sizeof(uint32_t) * (framebuffer_size + DVI_N_TMDS_BUFFERS * self->tmdsbuf_size);

[dhalbert]

Thanks!