i965: Fix encode_slm_size() to take a generation, not a device info.

i965: Fix encode_slm_size() to take a generation, not a device info.

In the Vulkan driver, we have the generation number (a compile time
constant) but not necessarily the brw_device_info struct.  I meant
to rework the function to take a generation number instead of a
brw_device_info pointer to accomodate this.  But I forgot, and left
it taking a brw_device_info pointer, while making Vulkan pass the
generation number (8, 9, ...) directly.  This led to crashes.

Brown paper bag fix for commit 87d062a94080373995170f51063a9649.

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96504
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>