drm/radeon: take ownership of pipe initialization

Take ownership of pipe initialization away from KFD.

Note that hpd_eop_gpu_addr was already large enough to accomodate all
pipes.

Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>