drm/i915/perf: fix flex eu registers programming

drm/i915/perf: fix flex eu registers programming

We were reserving fewer dwords in the ring than necessary. Indeed
we're always writing all registers once, so discard the actual number
of registers given by the user and just program the whitelisted ones
once.

Fixes: 4c2fae652a4a ("drm/i915/perf: Add OA unit support for Gen 8+")
Reported-by: Matthew Auld <matthew.william.auld@gmail.com>
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Cc: <stable@vger.kernel.org> # v4.12+
Link: https://patchwork.freedesktop.org/patch/msgid/20170803165812.2373-6-lionel.g.landwerlin@intel.com
(cherry picked from commit 01d928e9a1644eb2e28f684905f888e700c7b9dc)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>