intel: Fix broxton 2x6 way size computation

This patch is undoing the changes to way size computation
in broxton 2x6, made by below commit:

Commit: 0d576fbfbe
Author:     Anuj Phogat <anuj.phogat@gmail.com>
i965: Simplify l3 way size computations

By making use of l3_banks field in gen_device_info struct
l3_way_size for gen7+ = 2 * l3_banks.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101306
Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Tested-by: Mark Janes <mark.a.janes@intel.com>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>

src/intel/common/gen_l3_config.c

@@ -255,6 +255,10 @@ static unsigned
 get_l3_way_size(const struct gen_device_info *devinfo)
 {
    assert(devinfo->l3_banks);
+
+   if (devinfo->is_broxton)
+      return 4;
+
    return 2 * devinfo->l3_banks;
 }