Your /var/log/Xorg.0.log output confrims what oldcpu suspected - the fbdev driver is being loaded, and the radeonhd/radeon drivers are not used. This needs to be solved first.
Code:
[ 32.496] (II) Loading /usr/lib64/xorg/modules/drivers/fbdev_drv.so
[ 32.496] (II) Loading /usr/lib64/xorg/modules/libfbdevhw.so
[ 32.497] (**) FBDEV(0): claimed PCI slot 0@0:1:0
[ 32.497] (II) FBDEV(0): using default device
[ 32.497] (WW) Falling back to old probe method for vesa
[ 32.497] (II) FBDEV(0): Creating default Display subsection in Screen section
"Default Screen Section" for depth/fbbpp 24/32
[ 32.497] (==) FBDEV(0): Depth 24, (==) framebuffer bpp 32
[ 32.497] (==) FBDEV(0): RGB weight 888
[ 32.497] (==) FBDEV(0): Default visual is TrueColor
[ 32.497] (==) FBDEV(0): Using gamma correction (1.0, 1.0, 1.0)
[ 32.497] (II) FBDEV(0): hardware: radeondrmfb (video memory: 8100kB)
[ 32.497] (II) FBDEV(0): checking modes against framebuffer device...
[ 32.497] (II) FBDEV(0): checking modes against monitor...
[ 32.497] (--) FBDEV(0): Virtual size is 1920x1080 (pitch 1920)
[ 32.497] (**) FBDEV(0): Built-in mode "current"
[ 32.497] (==) FBDEV(0): DPI set to (96, 96)
[ 32.497] (II) Loading sub module "fb"
[ 32.497] (II) LoadModule: "fb"
[ 32.498] (II) Loading /usr/lib64/xorg/modules/libfb.so
[ 32.506] (II) Module fb: vendor="X.Org Foundation"
[ 32.506] compiled for 1.10.4, module version = 1.0.0
[ 32.506] ABI class: X.Org ANSI C Emulation, version 0.4
[ 32.506] (**) FBDEV(0): using shadow framebuffer
[ 32.507] (II) Loading sub module "shadow"
[ 32.507] (II) LoadModule: "shadow"
[ 32.507] (II) Loading /usr/lib64/xorg/modules/libshadow.so
[ 32.508] (II) Module shadow: vendor="X.Org Foundation"
[ 32.508] compiled for 1.10.4, module version = 1.1.0
[ 32.508] ABI class: X.Org ANSI C Emulation, version 0.4
[ 32.508] (II) UnloadModule: "radeonhd"
[ 32.508] (II) Unloading radeonhd
[ 32.508] (II) UnloadModule: "radeon"
[ 32.508] (II) Unloading radeon
[ 32.508] (II) UnloadModule: "vesa"
[ 32.508] (II) Unloading vesa
[ 32.508] (==) Depth 24 pixmap format is 32 bpp
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