drm/i915/gvt: parse init context to update cmd accessible reg whitelist

drm/i915/gvt: parse init context to update cmd accessible reg whitelist

Logical Context is actually a big batch buffer consisting of multiple
LRI commands + saved registers. It comprises Ring Context (the first
0x50 dwords) and Engine Context. The registers defined in Engine Context
are command accessible, and safe to execute in VM Context.
However, not all of them are currently tracked in existing register
whitelist. Here we kick hardware to generate a dummy Engine Context and
then scan the dummy Engine context to update whitelist dynamically. Based
on updated list, later patches will audit future VM Engine Contexts to
disallow undesired LRIs (if out of what hardware generates).

Cc: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Wang Zhi <zhi.a.wang@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20201223034430.16934-1-yan.y.zhao@intel.com
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>