video: Drop CONFIG_LCD_BMP_RLE8

This is not defined by any board. Even sandbox doesn't actually use
it since it has migrated to DM_VIDEO.

Drop this option. Remove the dead code also, for completeness, even
though the whole lcd.c file will be dropped soon.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Anatolij Gustschin <agust@denx.de>