The PLBU expects the viewport's 4 borders' coordinates, however
currently we're feeding the coordinate of the left-bottom point and the
size to it, which leads to misrendering when the left-bottom point is
not (0,0).

Change the macros for the viewport PLBU command, and the data feed to
it. The code to calculate the 4 borders is ported from Panfrost.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Qiang Yu <yuq825@gmail.com>