drm/msm/a6xx+: Don't let IB_SIZE overflow

IB_SIZE is only b0..b19.  Starting with a6xx gen3, additional fields
were added above the IB_SIZE.  Accidentially setting them can cause
badness.  Fix this by properly defining the CP_INDIRECT_BUFFER packet
and using the generated builder macro to ensure unintended bits are not
set.

v2: add missing type attribute for IB_BASE
v3: fix offset attribute in xml

Reported-by: Connor Abbott <cwabbott0@gmail.com>
Fixes: a83366ef ("drm/msm/a6xx: add A640/A650 to gpulist")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/643396/