staging: fbtft: add tearing signal detect

For st7789v IC, when we need continuous full screen refresh, it is best to
wait for the tearing effect line signal to arrive to avoid screen tearing.

Signed-off-by: Carlis <zhangxuezhi1@yulong.com>
Link: https://lore.kernel.org/r/1612706517-124617-1-git-send-email-zhangxuezhi3@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>