staging: fbtft: use MIPI DCS for ST7789V and C-Berry28

This patch makes use of the standard MIPI Display Command Set to remove
redundant entries from the command enum of the ST7789V display controller
and also some of the magic constants found in the init sequence of the
C-Berry28 display.

Signed-off-by: Dennis Menschel <menschel-d@posteo.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>