intel/tools: Fix detection of enabled shader stages.

We renamed "Function Enable" to "Enable", which broke our detection
of whether shaders are enabled or not.  So, we'd see a bunch of HS/DS
packets with program offsets of 0, and think that was a valid TCS/TES.

Fixes: c032cae9 (genxml: Rename "Function Enable" to "Enable".)

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit 9a0465b3)