drm/amdkfd: Fix sdma queue allocate race condition

SDMA queue allocation requires the dqm lock at it modify
the global dqm members. Move up the dqm_lock so sdma
queue allocation is enclosed in the critical section. Move
mqd allocation out of critical section to avoid circular
lock dependency.

Signed-off-by: Oak Zeng <Oak.Zeng@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>