Bug#878221: linux-image-4.9.0-4-amd64: Screen flickers randomly with Radeon R9 270X since upgrade from 4.9.0-3 to 4.9.0-4

[Paul Boekholt <pboekholt@patient1.nl>]

Same issue.

eDP-1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 344mm x 193mm
DP-1 connected 1920x1080+1366+0 (normal left inverted right x axis y axis) 480mm x 270mm

00:02.0 VGA compatible controller: Intel Corporation HD Graphics 5500 (rev 09) (prog-if 00 [VGA controller])
	Subsystem: ASUSTeK Computer Inc. HD Graphics 5500
	Flags: bus master, fast devsel, latency 0, IRQ 50
	Memory at b1000000 (64-bit, non-prefetchable) [size=16M]
	Memory at c0000000 (64-bit, prefetchable) [size=256M]
	I/O ports at 4000 [size=64]
	[virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
	Capabilities: <access denied>
	Kernel driver in use: i915
	Kernel modules: i915

4.9.0-3 works, 4.9.0-4 causes flickering after a while when a key is pressed.