i965: Add brw_device_info::min_ds_entries field.

i965: Add brw_device_info::min_ds_entries field.

From the 3DSTATE_URB_DS documentation:

"Project: IVB, HSW
 If Domain Shader Thread Dispatch is Enabled then the minimum number of
 handles that must be allocated is 10 URB entries."

"Project: BDW+
 If Domain Shader Thread Dispatch is Enabled then the minimum number of
 handles that must be allocated is 34 URB entries."

When the HS is run in SINGLE_PATCH mode (the only mode we support
today), there is no minimum for HS - it's just zero.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>