[BUG] 4.17-rcX delays during boot and memory mapping errors

[Bob Tracy <rct@gherkin.frus.com>]

Apologies for not having more in the way of diagnostic info.

Every one of the 4.17-rcX series has hung during boot at the point where
"acpid" starts up.  Beginning with -rc5, the boot actually proceeds to
completion after an "uncomfortably" long delay.

Attempting to run the X11 server results in the following diagnostic
output in "/var/log/Xorg.0.log":

(...)
[   109.951] (--) Depth 24 pixmap format is 32 bpp
[   109.951] (II) RADEON(0): [DRI2] Setup complete
[   109.951] (II) RADEON(0): [DRI2]   DRI driver: r600
[   109.951] (II) RADEON(0): [DRI2]   VDPAU driver: r600
[   109.951] Failed to map cursor buffer memory
[   109.951] Failed to map cursor buffer memory
[   109.951] Failed to map cursor buffer memory
[   109.952] Failed to map cursor buffer memory
[   109.952] Failed to map cursor buffer memory
[   109.952] Failed to map cursor buffer memory
[   109.952] (II) RADEON(0): Front buffer size: 8160K
[   109.952] (II) RADEON(0): VRAM usage limit set to 218167K
[   109.952] (==) RADEON(0): DRI3 disabled
[   109.952] (==) RADEON(0): Backing store enabled
[   109.952] (II) RADEON(0): Direct rendering enabled
[   109.952] (II) EXA(0): Driver allocated offscreen pixmaps
[   109.952] (II) EXA(0): Driver registered support for the following
operations:
[   109.952] (II)         Solid
[   109.952] (II)         Copy
[   109.952] (II)         Composite (RENDER acceleration)
[   109.952] (II)         UploadToScreen
[   109.952] (II)         DownloadFromScreen
[   109.952] (EE) 
Fatal server error:
[   109.952] (EE) failed to map shader -75
[   109.952] (EE) 
[   109.952] (EE) 
Please consult the The X.Org Foundation support 
         at http://wiki.x.org
 for help. 
[   109.952] (EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
[   109.952] (EE) 
[   109.971] (EE) Server terminated with error (1). Closing log file.

Everything works normally with a 4.16 kernel.

--Bob