[PATCH RESEND] drm/aspeed: fix Kconfig warning & subsequent build errors

[Randy Dunlap]

kernel test robot reported build errors (undefined references)
that didn't make much sense. After reproducing them, there is also
a Kconfig warning that is the root cause of the build errors, so
fix that Kconfig problem.

Fixes this Kconfig warning:
WARNING: unmet direct dependencies detected for CMA
  Depends on [n]: MMU [=n]
  Selected by [m]:
  - DRM_ASPEED_GFX [=m] && HAS_IOMEM [=y] && DRM [=m] && OF [=y] && (COMPILE_TEST [=y] || ARCH_ASPEED) && HAVE_DMA_CONTIGUOUS [=y]

and these dependent build errors:
(.text+0x10c8c): undefined reference to `start_isolate_page_range'
microblaze-linux-ld: (.text+0x10f14): undefined reference to `test_pages_isolated'
microblaze-linux-ld: (.text+0x10fd0): undefined reference to `undo_isolate_page_range'

Fixes: 76356a966e33 ("drm: aspeed: Clean up Kconfig options")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Joel Stanley <joel@xxxxxxxxx>
Cc: Andrew Jeffery <andrew@xxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Michal Simek <monstr@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-aspeed@xxxxxxxxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: David Airlie <airlied@xxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
---
First sent on 2020-09-07.
Feel free to fix the Kconfig warning some other way...

 drivers/gpu/drm/aspeed/Kconfig |    1 +
 1 file changed, 1 insertion(+)

--- linux-next-20201009.orig/drivers/gpu/drm/aspeed/Kconfig
+++ linux-next-20201009/drivers/gpu/drm/aspeed/Kconfig
@@ -3,6 +3,7 @@ config DRM_ASPEED_GFX
 	tristate "ASPEED BMC Display Controller"
 	depends on DRM && OF
 	depends on (COMPILE_TEST || ARCH_ASPEED)
+	depends on MMU
 	select DRM_KMS_HELPER
 	select DRM_KMS_CMA_HELPER
 	select DMA_CMA if HAVE_DMA_CONTIGUOUS