drm/i915/gvt: adjust to fixed vGPU types

Previous vGPU type create tried to determine vGPU type name e.g _1, _2
based on the number of mdev devices can be created, but different type
might have very different resource size depending on physical device.
We need to split type name vs. actual mdev resource and create fixed
vGPU type with determined size for consistence.

With this we'd like to fix vGPU types for _1, _2, _4 and _8 now, each
type has fixed defined resource size. Available mdev instances that could
be created is determined by physical resource, and user should query
for that before creating.

Cc: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>