drm/amdkfd: fix cu mask for asics with wgps

GFX10 and up have work group processors (WGP) and WGP mode is the native
compile mode.

KFD and ROCr have no visibility into whether a dispatch is operating
in CU or WGP mode.

Enforce CU masking to be pairwise continguous in enablement and
round robin distribute CUs across the SEs in a pairwise manner to
assume WGP mode at all times.

Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>