Send multiple bytes in case of updating epaper

[psiegl]

In case the E-Ink display 4.0' shall be updated with new content, today the logic sets DC to 1, CS to 0, then sends 1 Byte (8 bits) and subsequently sets CS to 1. This procedure happens for all 8 bits of data to be pushed into the display. However, one can also send a burst of data as long as CS is 0 and DC 1. This works smoothly for the command 0x10, which seems to be the command to push the epaper content.