drm/amd/display: fix S/G display enablement

An assignment statement was reversed during a refactor which effectively
disabled S/G display outright. Since, we use
adev->mode_info.gpu_vm_support to indicate to the rest of the driver
that S/G display should be enabled and currently it is always set to
false. So, to fix this set adev->mode_info.gpu_vm_support's value to
that of init_data.flags.gpu_vm_support (and not vice versa).

Fixes: 098c1307 ("drm/amd/display: enable S/G display for for recent APUs by default")
Reported-by: Mark Broadworth <mark.broadworth@amd.com>
Tested-by: Mark Broadworth <mark.broadworth@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>