drm/amdkfd: switch over to using drm_exec v3

Avoids quite a bit of logic and kmalloc overhead.

v2: fix multiple problems pointed out by Felix
v3: two more nit picks from Felix fixed

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230711133122.3710-4-christian.koenig@amd.com