1) Adapt to vulkan:
Now use double SWITCH BUFFER to replace the 128 nops w/a,
because when vulkan introduced, umd can insert 7 ~ 16 IBs
per submit which makes 256 DW size cannot hold the whole
DMAframe (if we still insert those 128 nops), CP team suggests
use double SWITCH_BUFFERs, instead of tricky 128 NOPs w/a.

2) To fix the CE VM fault issue when MCBP introduced:
Need one more COND_EXEC wrapping IB part (original one us
for VM switch part).

this change can fix vm fault issue caused by below scenario
without this change:

>CE passed original COND_EXEC (no MCBP issued this moment),
 proceed as normal.

>DE catch up to this COND_EXEC, but this time MCBP issued,
 thus DE treats all following packages as NOP. The following
 VM switch packages now looks just as NOP to DE, so DE
 dosen't do VM flush at all.

>Now CE proceeds to the first IBc, and triggers VM fault,
 because DE didn't do VM flush for this DMAframe.

3) change estimated alloc size for gfx9.
with new DMAframe scheme, we need modify emit_frame_size
for gfx9

4) No need to insert 128 nops after gfx8 vm flush anymore
because there was double SWITCH_BUFFER append to vm flush,
and for gfx7 we already use double SWITCH_BUFFER following
after vm_flush so no change needed for it.

5) Change emit_frame_size for gfx8

v2: squash in BUG removal from Monk
Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>