video/fbdev/stifb: Implement the stifb_fillrect() function

video/fbdev/stifb: Implement the stifb_fillrect() function

BugLink: https://bugs.launchpad.net/bugs/1998843
[ Upstream commit 9c379c65241707e44072139d782bc2dfec9b4ab3 ]

The stifb driver (for Artist/HCRX graphics on PA-RISC) was missing
the fillrect function.
Tested on a 715/64 PA-RISC machine and in qemu.

Signed-off-by: Helge Deller <deller@gmx.de>
Stable-dep-of: 776d875fd4cb ("fbdev: stifb: Fall back to cfb_fillrect() on 32-bit HCRX cards")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>